Java - 4.056s official score
The main idea of this is to never allocate memory when it is not needed. The only exception are primitives, which should be optimized by the compiler anyway. Everything else is stored as masks and arrays of operations done in each step, which can be undone when the recursion step is completed.
About half of all sudokus are solved completely without backtracking, but if I push that number higher the overall time seems to be slower. I'm planning om rewriting this in C++ and optimize even further, but this solver is becoming a behemoth.
I wanted to implement as much caching as possible, which lead to some issues. For example, if there are two cells on the same row which can only have the number 6, then we have reached an impossible case, and should return to the backtracking. But since I calculated all options in one sweep, and then placed numbers in cells with only one possibility, I didn't double check that I had placed a number in the same row just before. This lead to impossible solutions.
With everything being contained in the arrays defined at the top, the memory usage of the actual solver is about 216kB. The main part of the memory usage comes from the array containing all the puzzles, and the I/O handlers in Java.
EDIT: I have a version which is translated to C++ now, but it isn't vastly faster. The official time is around 3.5 seconds, which isn't a huge improvement. I think the main issue with my implementation is that I keep my masks as arrays rather than bitmasks. I'll try to analyze Arnauld's solution to see what can be done to improve it.
import java.util.HashMap;
import java.util.ArrayList;
import java.util.Arrays;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.File;
import java.io.PrintWriter;
public class Sudoku {
final private int[] unsolvedBoard;
final private int[] solvedBoard;
final private int[][] neighbors;
final private int[][] cells;
private static int[] clues;
final private int[][] mask;
final private int[] formattedMask;
final private int[][] placedMask;
final private boolean[][][] lineMask;
final private int[] lineCounters;
final private int[][] sectionCounters;
final private int[][] sectionMask;
private int easySolved;
private boolean isEasy;
private int totEasy;
private int placedNumbers;
public long totTime = 0;
private boolean solutionFound;
public long lastPrint;
private boolean shouldPrint;
private boolean isImpossible = false;
public Sudoku() {
mask = new int[81][9];
formattedMask = new int[81];
placedMask = new int[64][64];
lineMask = new boolean[64][81][9];
sectionCounters = new int[9][27];
sectionMask = new int[9][27];
lineCounters = new int[64];
neighbors = new int[81][20];
unsolvedBoard = new int[81];
solvedBoard = new int[81];
cells = new int[][] {{0 ,1 ,2 ,9 ,10,11,18,19,20},
{3 ,4 ,5 ,12,13,14,21,22,23},
{6 ,7 ,8 ,15,16,17,24,25,26},
{27,28,29,36,37,38,45,46,47},
{30,31,32,39,40,41,48,49,50},
{33,34,35,42,43,44,51,52,53},
{54,55,56,63,64,65,72,73,74},
{57,58,59,66,67,68,75,76,77},
{60,61,62,69,70,71,78,79,80}};
}
final public long solveSudoku(int[] board, int clue) {
long t1 = 0,t2 = 0;
t1 = System.nanoTime();
System.arraycopy(board, 0, unsolvedBoard, 0, 81);
System.arraycopy(board, 0, solvedBoard, 0, 81);
placedNumbers = 0;
solutionFound = false;
isEasy = true;
isImpossible = false;
for (int[] i : mask) {
Arrays.fill(i, 0);
}
for (boolean[][] i : lineMask) {
for (boolean[] j : i) {
Arrays.fill(j, false);
}
}
for (int i = 0; i < 81; i++) {
if (solvedBoard[i] != -1) {
put(i, solvedBoard[i]);
placedNumbers++;
}
}
solve(0, 0);
t2 = System.nanoTime();
easySolved += isEasy ? 1 : 0;
if (solutionFound && placedNumbers == 81) {
totTime += t2-t1;
if (shouldPrint || t2-t1 > 5*1_000_000_000L) {
System.out.print(String.format(
"Solution from %2d clues found in %7s",
clue,
printTime(t1, t2)
));
shouldPrint = false;
if (t2-t1 > 1*1000_000_000L) {
System.out.println();
display2(board, solvedBoard);
}
}
} else {
System.out.println("No solution");
display2(unsolvedBoard, solvedBoard);
return -1;
}
return t2 - t1;
}
final private void solve(int v, int vIndex) {
lineCounters[vIndex] = 0;
int easyIndex = placeEasy(vIndex);
if (isImpossible) {
resetEasy(vIndex, easyIndex);
resetLineMask(vIndex);
return;
}
if (placedNumbers == 81) {
solutionFound = true;
return;
}
// if (true) {
// return;
// }
// either get the next empty cell
// while (v < 81 && solvedBoard[v] >= 0) {
// v++;
// }
// or get the cell with the fewest options
generateFormattedMasks();
int minOptions = 9;
for (int i = 0; i < 81; i++) {
int options = formattedMask[i] & 0xffff;
if (options > 0 && options < minOptions) {
minOptions = options;
v = i;
}
if (options == 0 && solvedBoard[i] == -1) {
isImpossible = true;
}
}
if (!isImpossible) {
for (int c = 0; c < 9; c++) {
if (isPossible(v, c)) {
isEasy = false;
put(v, c);
placedNumbers++;
solve(v + 1, vIndex + 1);
if (solutionFound) {
return;
}
unput(v, c);
placedNumbers--;
}
}
}
resetEasy(vIndex, easyIndex);
resetLineMask(vIndex);
}
final private void resetEasy(int vIndex, int easyIndex) {
for (int i = 0; i < easyIndex; i++) {
int tempv2 = placedMask[vIndex][i];
int c2 = solvedBoard[tempv2];
unput(tempv2, c2);
placedNumbers--;
}
}
final private void resetLineMask(int vIndex) {
if (lineCounters[vIndex] > 0) {
for (int i = 0; i < 81; i++) {
for (int c = 0; c < 9; c++) {
if (lineMask[vIndex][i][c]) {
enable(i, c);
lineMask[vIndex][i][c] = false;
}
}
}
}
isImpossible = false;
}
final private int placeEasy(int vIndex) {
int easyIndex = 0;
int lastPlaced = 0, tempPlaced = 0, easyplaced = 0;
int iter = 0;
while (placedNumbers > lastPlaced+1) {
lastPlaced = placedNumbers;
tempPlaced = 0;
while (placedNumbers > tempPlaced + 5) {
tempPlaced = placedNumbers;
easyIndex = placeNakedSingles(vIndex, easyIndex);
if (isImpossible) {
return easyIndex;
}
}
tempPlaced = 0;
while (placedNumbers < 55*1 && placedNumbers > tempPlaced + 2) {
tempPlaced = placedNumbers;
easyIndex = placeHiddenSingles(vIndex, easyIndex);
if (isImpossible) {
return easyIndex;
}
}
tempPlaced = 0;
while (placedNumbers < 65*1 && placedNumbers > tempPlaced + 1) {
tempPlaced = placedNumbers;
easyIndex = placeNakedSingles(vIndex, easyIndex);
if (isImpossible) {
return easyIndex;
}
}
if (iter < 2 && placedNumbers < 55*1) {
checkNakedTriples(vIndex);
}
if (placedNumbers < 45*1) {
checkNakedDoubles(vIndex);
identifyLines(vIndex);
}
iter++;
}
return easyIndex;
}
final private int placeNakedSingles(int vIndex, int easyIndex) {
generateFormattedMasks();
for (int tempv = 0; tempv < 81; tempv++) {
int possibilities = formattedMask[tempv];
if ((possibilities & 0xffff) == 1) {
possibilities >>= 16;
int c = 0;
while ((possibilities & 1) == 0) {
possibilities >>= 1;
c++;
}
if (isPossible(tempv, c)) {
put(tempv, c);
placedMask[vIndex][easyIndex++] = tempv;
placedNumbers++;
} else {
isImpossible = true;
return easyIndex;
}
} else if (possibilities == 0 && solvedBoard[tempv] == -1) {
isImpossible = true;
return easyIndex;
}
}
return easyIndex;
}
final private int placeHiddenSingles(int vIndex, int easyIndex) {
for (int[] i : sectionCounters) {
Arrays.fill(i, 0);
}
for (int c = 0; c < 9; c++) {
for (int v = 0; v < 81; v++) {
if (isPossible(v, c)) {
int cell = 3 * (v / 27) + ((v / 3) % 3);
sectionCounters[c][v / 9]++;
sectionCounters[c][9 + (v % 9)]++;
sectionCounters[c][18 + cell]++;
sectionMask[c][v / 9] = v;
sectionMask[c][9 + (v % 9)] = v;
sectionMask[c][18 + cell] = v;
}
}
int v;
for (int i = 0; i < 9; i++) {
if (sectionCounters[c][i] == 1) {
v = sectionMask[c][i];
if (isPossible(v, c)) {
put(v, c);
placedMask[vIndex][easyIndex++] = v;
placedNumbers++;
int cell = 3 * (v / 27) + ((v / 3) % 3);
sectionCounters[c][9 + (v%9)] = 9;
sectionCounters[c][18 + cell] = 9;
} else {
isImpossible = true;
return easyIndex;
}
}
}
for (int i = 9; i < 18; i++) {
if (sectionCounters[c][i] == 1) {
v = sectionMask[c][i];
if (isPossible(v, c)) {
put(v, c);
placedMask[vIndex][easyIndex++] = v;
int cell = 3 * (v / 27) + ((v / 3) % 3);
placedNumbers++;
sectionCounters[c][18 + cell]++;
} else {
isImpossible = true;
return easyIndex;
}
}
}
for (int i = 18; i < 27; i++) {
if (sectionCounters[c][i] == 1) {
v = sectionMask[c][i];
if (isPossible(v, c)) {
put(v, c);
placedMask[vIndex][easyIndex++] = v;
placedNumbers++;
} else {
isImpossible = true;
return easyIndex;
}
}
}
}
return easyIndex;
}
final private int getFormattedMask(int v) {
if (solvedBoard[v] >= 0) {
return 0;
}
int x = 0;
int y = 0;
for (int c = 8; c >= 0; c--) {
x <<= 1;
x += mask[v][c] == 0 ? 1 : 0;
y += mask[v][c] == 0 ? 1 : 0;
}
x <<= 16;
return x + y;
}
final private int getCachedMask(int v) {
return formattedMask[v];
}
final private void generateFormattedMasks() {
for (int i = 0; i < 81; i++) {
formattedMask[i] = getFormattedMask(i);
}
}
final private void generateFormattedMasks(int[] idxs) {
for (int i : idxs) {
formattedMask[i] = getFormattedMask(i);
}
}
final private void checkNakedDoubles(int vIndex) {
generateFormattedMasks();
for (int i = 0; i < 81; i++) {
int bitmask = formattedMask[i];
if ((bitmask & 0xffff) == 2) {
for (int j = i+1; j < (i/9+1)*9; j++) {
int bitmask_j = formattedMask[j];
if (bitmask == bitmask_j) {
bitmask >>= 16;
int c0, c1, k = 0;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c0 = k;
bitmask >>= 1;
k++;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c1 = k;
for (int cell = (i/9)*9; cell < (i/9+1)*9; cell++) {
if (cell != i && cell != j) {
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
for (int idx = 0; idx < 81; idx++) {
int i = (idx%9)*9 + idx/9;
int bitmask = formattedMask[i];
if ((bitmask & 0xffff) == 2) {
for (int j = i+9; j < 81; j += 9) {
int bitmask_j = formattedMask[j];
if (bitmask == bitmask_j) {
bitmask >>= 16;
int c0, c1, k = 0;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c0 = k;
bitmask >>= 1;
k++;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c1 = k;
for (int cell = i % 9; cell < 81; cell += 9) {
if (cell != i && cell != j) {
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
for (int idx = 0; idx < 9; idx++) {
for (int i = 0; i < 9; i++) {
int bitmask = formattedMask[cells[idx][i]];
if ((bitmask & 0xffff) == 2) {
for (int j = i+1; j < 9; j++) {
int bitmask_j = formattedMask[cells[idx][j]];
if (bitmask == bitmask_j) {
bitmask >>= 16;
int c0, c1, k = 0;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c0 = k;
bitmask >>= 1;
k++;
while ((bitmask & 1) == 0) {
k++;
bitmask >>= 1;
}
c1 = k;
for (int cellIdx = 0; cellIdx < 9; cellIdx++) {
if (cellIdx != i && cellIdx != j) {
int cell = cells[idx][cellIdx];
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
}
}
final private void checkNakedTriples(int vIndex) {
generateFormattedMasks();
for (int i = 0; i < 81; i++) {
int bitmask = formattedMask[i];
if ((bitmask & 0xffff) == 3) {
for (int j = i+1; j < (i/9+1)*9; j++) {
int bitmask_j = formattedMask[j];
if (bitmask_j > 0 && bitmask == (bitmask | bitmask_j)) {
for (int k = j+1; k < (i/9+1)*9; k++) {
int bitmask_k = formattedMask[k];
if (bitmask_k > 0 && bitmask == (bitmask | bitmask_k)) {
int bitmask_shifted = bitmask >> 16;
int c0, c1, c2, l = 0;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c0 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c1 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c2 = l;
for (int cell = (i/9)*9; cell < (i/9+1)*9; cell++) {
if (cell != i && cell != j && cell != k) {
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c2]) {
disable(cell, c2);
lineMask[vIndex][cell][c2] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
}
}
for (int idx = 0; idx < 81; idx++) {
int i = (idx%9)*9 + idx/9;
int bitmask = formattedMask[i];
if ((bitmask & 0xffff) == 3) {
for (int j = i+9; j < 81; j += 9) {
int bitmask_j = formattedMask[j];
if (bitmask_j > 0 && bitmask == (bitmask | bitmask_j)) {
for (int k = j+9; k < 81; k += 9) {
int bitmask_k = formattedMask[k];
if (bitmask_k > 0 && bitmask == (bitmask | bitmask_k)) {
int bitmask_shifted = bitmask >> 16;
int c0, c1, c2, l = 0;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c0 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c1 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c2 = l;
for (int cell = i%9; cell < 81; cell += 9) {
if (cell != i && cell != j && cell != k) {
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c2]) {
disable(cell, c2);
lineMask[vIndex][cell][c2] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
}
}
for (int idx = 0; idx < 9; idx++) {
for (int i = 0; i < 9; i++) {
int bitmask = formattedMask[cells[idx][i]];
if ((bitmask & 0xffff) == 3) {
for (int j = i+1; j < 9; j++) {
int bitmask_j = formattedMask[cells[idx][j]];
if (bitmask_j > 0 && bitmask == (bitmask | bitmask_j)) {
for (int k = j+1; k < 9; k++) {
int bitmask_k = formattedMask[cells[idx][k]];
if (bitmask_k > 0 && bitmask == (bitmask | bitmask_k)) {
int bitmask_shifted = bitmask >> 16;
int c0, c1, c2, l = 0;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c0 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c1 = l;
bitmask_shifted >>= 1;
l++;
while ((bitmask_shifted & 1) == 0) {
l++;
bitmask_shifted >>= 1;
}
c2 = l;
for (int cellIdx = 0; cellIdx < 9; cellIdx++) {
if (cellIdx != i && cellIdx != j && cellIdx != k) {
int cell = cells[idx][cellIdx];
if (!lineMask[vIndex][cell][c0]) {
disable(cell, c0);
lineMask[vIndex][cell][c0] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c1]) {
disable(cell, c1);
lineMask[vIndex][cell][c1] = true;
lineCounters[vIndex]++;
}
if (!lineMask[vIndex][cell][c2]) {
disable(cell, c2);
lineMask[vIndex][cell][c2] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
}
}
}
}
final private void identifyLines(int vIndex) {
int disabledLines = 0;
int[][] tempRowMask = new int[3][9];
int[][] tempColMask = new int[3][9];
for (int i = 0; i < 9; i++) {
for (int c = 0; c < 9; c++) {
for (int j = 0; j < 3; j++) {
tempRowMask[j][c] = 0;
tempColMask[j][c] = 0;
}
for (int j = 0; j < 9; j++) {
if (mask[cells[i][j]][c] == 0) {
tempRowMask[j/3][c]++;
tempColMask[j%3][c]++;
}
}
int rowCount = 0;
int colCount = 0;
int rowIdx = -1, colIdx = -1;
for (int j = 0; j < 3; j++) {
if (tempRowMask[j][c] > 0) {
rowCount++;
rowIdx = j;
}
if (tempColMask[j][c] > 0) {
colCount++;
colIdx = j;
}
}
if (rowCount == 1) {
for (int j = (i/3)*3; j < (i/3 + 1)*3; j++) {
if (j != i) {
for (int k = rowIdx*3; k < (rowIdx+1)*3; k++) {
int cell = cells[j][k];
if (!lineMask[vIndex][cell][c]) {
disable(cell, c);
lineMask[vIndex][cell][c] = true;
lineCounters[vIndex]++;
}
}
}
}
}
if (colCount == 1) {
for (int j = i % 3; j < 9; j += 3) {
if (j != i) {
for (int k = colIdx; k < 9; k += 3) {
int cell = cells[j][k];
if (!lineMask[vIndex][cell][c]) {
disable(cell, c);
lineMask[vIndex][cell][c] = true;
lineCounters[vIndex]++;
}
}
}
}
}
}
}
}
final private boolean isPossible(int v, int c) {
return mask[v][c] == 0;
}
final private int checkMask(int[][] neighbors, int v, int c) {
int tempValue = 0;
for (int n : neighbors[v]) {
if (mask[n][c] > 0) {
tempValue++;
}
}
return tempValue;
}
final private void put(int v, int c) {
solvedBoard[v] = c;
for (int i : neighbors[v]) {
mask[i][c]++;
}
for (int i = 0; i < 9; i++) {
mask[v][i]++;
}
}
final private void disable(int v, int c) {
mask[v][c]++;
}
final private void unput(int v, int c) {
solvedBoard[v] = -1;
for (int i : neighbors[v]) {
mask[i][c]--;
}
for (int i = 0; i < 9; i++) {
mask[v][i]--;
}
}
final private void enable(int v, int c) {
// enables++;
mask[v][c]--;
}
public String getString(int[] board) {
StringBuilder s = new StringBuilder();
for (int i : board) {
s.append(i+1);
}
return s.toString();
}
public long getTime() {
return totTime;
}
public static String printTime(long t1, long t2) {
String unit = " ns";
if (t2-t1 > 10000) {
unit = " us";
t1 /= 1000; t2 /= 1000;
}
if (t2-t1 > 10000) {
unit = " ms";
t1 /= 1000; t2 /= 1000;
}
if (t2-t1 > 10000) {
unit = " seconds";
t1 /= 1000; t2 /= 1000;
}
return (t2-t1) + unit;
}
public void display(int[] board) {
for (int i = 0; i < 9; i++) {
if (i % 3 == 0) {
System.out.println("+-----+-----+-----+");
}
for (int j = 0; j < 9; j++) {
if (j % 3 == 0) {
System.out.print("|");
} else {
System.out.print(" ");
}
if (board[i*9+j] != -1) {
System.out.print(board[i*9+j]+1);
} else {
System.out.print(" ");
}
}
System.out.println("|");
}
System.out.println("+-----+-----+-----+");
}
public void display2(int[] board, int[] solved) {
for (int i = 0; i < 9; i++) {
if (i % 3 == 0) {
System.out.println("+-----+-----+-----+ +-----+-----+-----+");
}
for (int j = 0; j < 9; j++) {
if (j % 3 == 0) {
System.out.print("|");
} else {
System.out.print(" ");
}
if (board[i*9+j] != -1) {
System.out.print(board[i*9+j]+1);
} else {
System.out.print(" ");
}
}
System.out.print("| ");
for (int j = 0; j < 9; j++) {
if (j % 3 == 0) {
System.out.print("|");
} else {
System.out.print(" ");
}
if (solved[i*9+j] != -1) {
System.out.print(solved[i*9+j]+1);
} else {
System.out.print(" ");
}
}
System.out.println("|");
}
System.out.println("+-----+-----+-----+ +-----+-----+-----+");
}
private boolean contains(int[] a, int v) {
for (int i : a) {
if (i == v) {
return true;
}
}
return false;
}
public void connect() {
for (int i = 0; i < 81; i++) {
for (int j = 0; j < 20; j++) {
neighbors[i][j] = -1;
}
}
int[] n_count = new int[81];
HashMap<Integer,ArrayList<Integer>> map
= new HashMap<Integer,ArrayList<Integer>>();
for (int[] c: cells) {
ArrayList<Integer> temp = new ArrayList<Integer>();
for (int v : c) {
temp.add(v);
}
for (int v : c) {
map.put(v,temp);
}
}
for (int i = 0; i < 81; i++) {
for (int j = (i/9)*9; j < (i/9)*9 + 9; j++) {
if (i != j) {
neighbors[i][n_count[i]++] = j;
}
}
for (int j = i%9; j < 81; j += 9) {
if (i != j) {
neighbors[i][n_count[i]++] = j;
}
}
for (int j : map.get(i)) {
if (i != j) {
if (!contains(neighbors[i], j)) {
neighbors[i][n_count[i]++] = j;
}
}
}
}
}
public static int[][] getInput(String filename) {
int[][] boards;
try (BufferedInputStream in = new BufferedInputStream(
new FileInputStream(filename))) {
BufferedReader r = new BufferedReader(
new InputStreamReader(in, StandardCharsets.UTF_8));
int n = Integer.valueOf(r.readLine());
boards = new int[n][81];
clues = new int[n];
for (int i = 0; i < n; i++) {
for (int j = 0; j < 81; j++) {
int x = r.read();
boards[i][j] = x - 49;
clues[i] += x > 48 ? 1 : 0;
}
r.read();
}
r.close();
} catch (IOException ex) {
throw new RuntimeException(ex);
}
return boards;
}
private int getTotEasy() {
return totEasy;
}
public String getSolution() {
StringBuilder s = new StringBuilder(256);
for (int i : unsolvedBoard) {
s.append(i+1);
}
s.append(",");
for (int i : solvedBoard) {
s.append(i+1);
}
return s.toString();
}
public static void main (String[] args) {
long t0 = System.nanoTime();
Sudoku gc = new Sudoku();
File f;
PrintWriter p;
try {
f = new File("sudoku_output.txt");
p = new PrintWriter(f);
} catch (Exception e) {
return;
}
if (args.length != 1) {
System.out.println("Usage: java Sudoku <input_file>");
return;
}
int[][] boards = gc.getInput(args[0]);
long tinp = System.nanoTime();
gc.connect();
long t1 = System.nanoTime();
p.println(boards.length);
long maxSolveTime = 0;
int maxSolveIndex = 0;
long[] solveTimes = new long[boards.length];
for (int i = 0; i < boards.length; i++) {
long tempTime = System.nanoTime();
if (tempTime - gc.lastPrint > 200_000_000
|| i == boards.length - 1) {
gc.shouldPrint = true;
gc.lastPrint = tempTime;
System.out.print(String.format(
"\r(%7d/%7d) ", i+1, boards.length));
}
long elapsed = gc.solveSudoku(boards[i], gc.clues[i]);
if (elapsed == -1) {
System.out.println("Impossible: " + i);
}
if (elapsed > maxSolveTime) {
maxSolveTime = elapsed;
maxSolveIndex = i;
}
solveTimes[i] = elapsed;
p.println(gc.getSolution());
// break;
}
p.close();
long t2 = System.nanoTime();
Arrays.sort(solveTimes);
System.out.println();
System.out.println("Median solve time: "
+ gc.printTime(0, solveTimes[boards.length/2]));
System.out.println("Longest solve time: "
+ gc.printTime(0, maxSolveTime) + " for board " + maxSolveIndex);
gc.display(boards[maxSolveIndex]);
System.out.println();
System.out.println("Total time (including prints): "
+ gc.printTime(t0,t2));
System.out.println("Sudoku solving time: "
+ gc.printTime(0,gc.getTime()));
System.out.println("Average time per board: "
+ gc.printTime(0,gc.getTime()/boards.length));
System.out.println("Number of one-choice digits per board: "
+ String.format("%.2f", gc.getTotEasy()/(double)boards.length));
System.out.println("Easily solvable boards: " + gc.easySolved);
System.out.println("\nInput time: " + gc.printTime(t0,tinp));
System.out.println("Connect time: " + gc.printTime(tinp,t1));
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
}
}
}
I have an APL+WIN solver but unless you have a copy of the interpreter on your machine you will have to count me out. For info your hard example took 30ms and the first easy example 16ms. – Graham – 2019-08-23T17:24:22.597
@Graham it took 30ms for all 49151 sudokus, or 30ms on average? – maxb – 2019-08-23T17:55:20.407
Sadly 30ms is for the hard example only. Unless this is worth pursuing I have only run the APL solver against your hard example and the first of the easy examples. If we can extrapolate from the hard example the we are looking at around 1500 seconds for the full set – Graham – 2019-08-23T18:28:24.527
@Graham Oh, now I understand what you mean. I could run it on my windows machine, but I think you should submit it and score it yourself, 1500 seconds is definitely not bad. – maxb – 2019-08-23T18:51:25.143
OK I will simply copy your example input file as APL array rather than creating a file and run it. Half an hour looks like the likely outcome. Here I must declare that this function is not entirely mine but an adaption of one created by another member of the APL community. – Graham – 2019-08-23T20:26:51.750
1Should the entries also be code golfed? Or... Can they be golfed, for the fun it? ;-) – The Matt – 2019-08-24T03:28:57.367
2@TheMatt I'd prefer non-golfed, just so I can verify that nothing fishy is going on – maxb – 2019-08-24T06:26:30.207
@maxb would you be willing to reveal the exact run time of your own solver? if it's not too different from 2.2s, it might be worth trying to improve the i/o of my (Arnauld's really) solution too – ngn – 2019-08-27T14:50:52.427
@ngn i haven't revealed that only because I'm still working on it (and I got beat). I'm in the 3.5-4s range with Java, I have some quirks to work out, and then I'll attempt to migrate it to C++ – maxb – 2019-08-27T15:49:21.503