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@@ -0,0 +1,59 @@
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+class Solution {
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+ private char[][] board;
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+ private int[] row;
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+ private int[] col;
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+ private int[] box;
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+
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+ public void solveSudoku(char[][] board) {
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+ this.board = board;
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+ row = new int[9];
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+ col = new int[9];
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+ box = new int[9];
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+ for (int i = 0; i < 9; i++) {
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+ for (int j = 0; j < 9; j++) {
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+ char c;
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+ if ((c = board[i][j]) == '.') continue;
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+ set(i, j, c - '0');
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+ }
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+ }
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+ dfs(0, 0);
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+ }
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+
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+ private boolean dfs(int y, int x) {
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+ for (; y < 9; y++) {
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+ for (x = x == 9 ? 0 : x; x < 9; x++) {
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+ char c;
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+ if ((c = board[y][x]) != '.') continue;
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+ int i = 1;
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+ for (; i <= 9; i++) {
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+ if (!set(y, x, i)) continue;
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+ if (dfs(y, x)) return true;
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+ unset(y, x);
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+ }
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+ if (i == 10) return false;
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+ }
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+ }
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+ return true;
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+ }
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+
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+ private boolean set(int y, int x, int val) {
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+ int mask = 1 << val;
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+ int id = y / 3 * 3 + x / 3;
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+ if ((row[y] & mask) != 0 || (col[x] & mask) != 0 || (box[id] & mask) != 0) return false;
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+ row[y] |= mask;
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+ col[x] |= mask;
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+ box[id] |= mask;
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+ board[y][x] = (char)(val + '0');
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+ return true;
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+ }
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+
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+ private void unset(int y, int x) {
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+ int val = board[y][x] - '0';
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+ int mask = (0x400 - 1) ^ (1 << val);
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+ int id = y / 3 * 3 + x / 3;
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+ row[y] &= mask;
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+ col[x] &= mask;
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+ box[id] &= mask;
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+ board[y][x] = '.';
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+ }
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+}
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