[Link] https://leetcode.com/problems/sudoku-solver/
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class Solution {
char[][] b;
public void solveSudoku(char[][] board) {
int len = board.length;
b = board;
solve();
}
boolean solve() {
for(int i = 0; i < 9; i++) {
for(int j = 0; j < 9; j++) {
if(b[i][j] == '.') {
for(char k = '1'; k <= '9'; k++) {
if(canput(i, j, k)) {
b[i][j] = k;
if(solve()) return true;
}
}
b[i][j] = '.';
return false;
}
}
}
return true;
}
boolean canput(int row, int col, char v) {
for(int i = 0; i < 9; i++) if(b[i][col] == v || b[row][i] == v) return false;
for(int si = 3 * (row / 3), i = si; i < si + 3; i++)
for(int sj = 3*(col/3), j = sj; j < sj + 3; j++) if(b[i][j] == v) return false;
return true;
}
}