[LeetCode]Sudoku Solver

题目描述

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

求解数独。

解题思路

用回溯法我们只要检查新加入的值能否在行、列以及小方块里有效即可。

代码

public static void solveSudoku(char[][] board) {internalSolveSudoku(board);}/** * 回溯求解数独问题 *  * @param board * @return */public static boolean internalSolveSudoku(char[][] board) {for (int i = 0; i < board.length; i++) {for (int j = 0; j < board[0].length; j++) {if (board[i][j] == '.') {for (int k = 1; k <= 9; k++) {board[i][j] = (char) ('0' + k);if (isValid(board, i, j)) {// 递归if (internalSolveSudoku(board)) {return true;}}// 回溯board[i][j] = '.';}return false;}}}return true;}/** * 判断一个数字在当前位置是否合法 *  * @param board * @param row * @param column * @return */public static boolean isValid(char[][] board, int row, int column) {int cellStartX = (row / 3) * 3;int cellStartY = (column / 3) * 3;char c = board[row][column];for (int i = 0; i < board.length; i++) {if (i != row && board[i][column] == c) {return false;}}for (int i = 0; i < board[0].length; i++) {if (i != column && board[row][i] == c) {return false;}}for (int i = cellStartX; i < cellStartX + 3; i++) {for (int j = cellStartY; j < cellStartY + 3; j++) {if (i != row && j != column && board[i][j] == c)return false;}}return true;}