LeetCode 037 Sudoku Solver
2024-09-02 06:13:53
题目要求：Sudoku Solver
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.
分析：
参考网址：http://www.cnblogs.com/panda_lin/archive/2013/11/04/sudoku_solver.html
回溯法尝试所有解0_o
① 对于每个空位'.'，遍历1~9，check合理之后递归；
② check的时候，不用遍历整个数独，只需检查加入的行、列和块就足够了。
代码如下：
class Solution {
public:
bool isValidSudoku(vector<vector<char> > &board, int x, int y) {
int row, col;
// Same value in the same column?
for (row = 0; row < 9; ++row) {
if ((x != row) && (board[row][y] == board[x][y])) {
return false;
}
}
// Same value in the same row?
for (col = 0; col < 9; ++col) {
if ((y != col) && (board[x][col] == board[x][y])) {
return false;
}
}
// Same value in the 3 * 3 block it belong to?
for (row = (x / 3) * 3; row < (x / 3 + 1) * 3; ++row) {
for (col = (y / 3) * 3; col < (y / 3 + 1) * 3; ++col) {
if ((x != row) && (y != col) && (board[row][col] == board[x][y])) {
return false;
}
}
}
return true;
}
bool internalSolveSudoku(vector<vector<char> > &board) {
for (int row = 0; row < 9; ++row) {
for (int col = 0; col < 9; ++col) {
if ('.' == board[row][col]) {
for (int i = 1; i <= 9; ++i) {
board[row][col] = '0' + i;
if (isValidSudoku(board, row, col)) {
if (internalSolveSudoku(board)) {
return true;
}
}
board[row][col] = '.';
}
return false;
}
}
}
return true;
}
void solveSudoku(vector<vector<char> > &board) {
internalSolveSudoku(board);
}
};
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