题目链接

【题解】

回溯法搞一下。
用set和数组下标判重。

【代码】

class Solution {
public:

    set<int> myset[9];
    int hang[9][10],lie[9][10];

    bool dfs(vector<vector<char>>& board,int x,int y){
        if (y==9){
            x++;y = 0;
        }
        if (x==9){
            return true;
        }
        if (board[x][y]!='.'){
            return dfs(board,x,y+1);
        }
        for (int i = 1;i <= 9;i++){
            if (hang[x][i] || lie[y][i]) continue;
            int idx = (x/3)*3+y/3;
            if (myset[idx].find(i)!=myset[idx].end()) continue;

            hang[x][i] = lie[y][i] = 1;
            myset[idx].insert(i);
            char key = i+'0';
            board[x][y] = key;
            if (dfs(board,x,y+1)) return true;
            board[x][y] = '.';
            hang[x][i] = lie[y][i] = 0;
            myset[idx].erase(i);
        }
        return false;
    }

    void solveSudoku(vector<vector<char>>& board) {
        for (int i = 0;i < 9;i++) myset[i].clear();
        memset(hang,0,sizeof hang);memset(lie,0,sizeof lie);

        for (int i = 0 ;i < 9;i++)
            for (int j = 0;j < 9;j++)
                if (board[i][j]!='.'){
                    int x = board[i][j]-'0';
                    hang[i][x]=1;
                    lie[j][x] = 1;
                    int ti = i/3,tj = j/3;
                    int idx = ti*3+tj;
                    myset[idx].insert(x);
                }

        dfs(board,0,0);
    }
};