LeetCode 37. Sudoku Solver
Solution1:
转载自花花酱:http://zxi.mytechroad.com/blog/searching/leetcode-37-sudoku-solver/
与之前的DFS套路题不大一样,注意!
class Solution {
public:
void solveSudoku(vector<vector<char>>& board) {
rows_ = vector<vector<int>>(9, vector<int>(10));
cols_ = vector<vector<int>>(9, vector<int>(10));
boxes_ = vector<vector<int>>(9, vector<int>(10));
//预先设置剪枝条件
for(int i = 0; i < 9; i++)
for(int j = 0; j < 9; j++) {
const char c = board[i][j];
if ( c != '.') {
int n = c - '0';
int bx = i / 3;
int by = j / 3;
rows_[i][n] = 1;
cols_[j][n] = 1;
boxes_[bx * 3 + by][n] = 1;
}
}
fill(board, 0, 0);
}
private:
vector<vector<int>> rows_, cols_, boxes_;
bool fill(vector<vector<char>>& board, int x, int y) {
if (x == 9)
return true;
int ny = (y + 1) % 9;
int nx = (ny == 0) ? x + 1 : x;
if (board[x][y] != '.') return fill(board, nx, ny);
for (int i = 1; i <= 9; i++) {
int bx = x / 3;
int by = y / 3;
int box_key = bx * 3 + by;
if (!rows_[x][i] && !cols_[y][i] && !boxes_[box_key][i]) {
rows_[x][i] = 1;
cols_[y][i] = 1;
boxes_[box_key][i] = 1;
board[x][y] = i + '0';
if (fill(board, nx, ny)) return true;
board[x][y] = '.';
boxes_[box_key][i] = 0;
cols_[y][i] = 0;
rows_[x][i] = 0;
}
}
return false;
}
};