[leetcode]37. Sudoku Solver@Java解题报告

https://leetcode.com/problems/sudoku-solver/description/

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.

package go.jacob.day803;/** * 37. Sudoku Solver * @author Jacob * 思路： * 简单地说思路就是循环处理子问题，对于每个格子，带入不同的9个数， * 然后判合法，如果成立就递归继续，结束后把数字设回'.' * */public class Demo1 {/* * 回溯法： *  */public void solveSudoku(char[][] board) {if (board == null || board.length == 0)return;solve(board);}private boolean solve(char[][] board) {for (int i = 0; i < board.length; i++) {for (int j = 0; j < board[0].length; j++) {if (board[i][j] == '.') {// 第一个'.'格一定是1-9中间的数for (char c = '1'; c <= '9'; c++) {if (isValid(board, i, j, c)) {board[i][j] = c;if (solve(board))return true;elseboard[i][j] = '.';}}/* * 如果能够运行到这里，说明这个位置不能确定具体的数字 */return false;}}}return true;}// 判断是否是一个正确的数独。方法与leetcode36. Valid Sudoku一致private boolean isValid(char[][] board, int row, int col, char c) {for (int i = 0; i < board.length; i++) {// 判断col列和row行是否满足数独条件if (board[i][col] == c || board[row][i] == c)return false;// 判断九宫格if (board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c)return false;}return true;}}