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package class28;
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public class Problem_0037_SudokuSolver {
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public static void solveSudoku(char[][] board) {
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boolean[][] row = new boolean[9][10];
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boolean[][] col = new boolean[9][10];
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boolean[][] bucket = new boolean[9][10];
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initMaps(board, row, col, bucket);
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process(board, 0, 0, row, col, bucket);
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}
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public static void initMaps(char[][] board, boolean[][] row, boolean[][] col, boolean[][] bucket) {
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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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int bid = 3 * (i / 3) + (j / 3);
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if (board[i][j] != '.') {
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int num = board[i][j] - '0';
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row[i][num] = true;
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col[j][num] = true;
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bucket[bid][num] = true;
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}
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}
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}
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}
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// 当前来到(i,j)这个位置，如果已经有数字，跳到下一个位置上
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// 如果没有数字，尝试1~9，不能和row、col、bucket冲突
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public static boolean process(char[][] board, int i, int j, boolean[][] row, boolean[][] col, boolean[][] bucket) {
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if (i == 9) {
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return true;
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}
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// 当离开(i，j)，应该去哪？(nexti, nextj)
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int nexti = j != 8 ? i : i + 1;
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int nextj = j != 8 ? j + 1 : 0;
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if (board[i][j] != '.') {
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return process(board, nexti, nextj, row, col, bucket);
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} else {
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// 可以尝试1~9
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int bid = 3 * (i / 3) + (j / 3);
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for (int num = 1; num <= 9; num++) { // 尝试每一个数字1~9
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if ((!row[i][num]) && (!col[j][num]) && (!bucket[bid][num])) {
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// 可以尝试num
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row[i][num] = true;
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col[j][num] = true;
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bucket[bid][num] = true;
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board[i][j] = (char) (num + '0');
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if (process(board, nexti, nextj, row, col, bucket)) {
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return true;
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}
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row[i][num] = false;
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col[j][num] = false;
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bucket[bid][num] = false;
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board[i][j] = '.';
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}
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}
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return false;
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}
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}
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}
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