数独填充 -- dfs,bitmasks

#include <bits/stdc++.h>

using i64 = long long;

struct node
{
    int x,y,row,col,grid,vis[3];
    node():x(0),y(0),row(0),col(0),grid(0){
        memset(vis,0,sizeof(vis));
    }
};
clock_t start,finish;
int c[10][10];
struct node d[10][10];
void output(){
    finish = clock();
    std::cout << std::fixed << std::setprecision(3) << (double)(finish - start) / (1000.0) << " s\n";
    for(int i = 1; i <= 9; i++){
        for(int j = 1; j <= 9; j++){
            std::cout << c[i][j] << " \n"[j == 9];
        }
    }
    
}

void updateRow(int x, int digit){
    int mask = (1 << digit);
    for(int i = 1; i <= 9; i++){
        d[x][i].row |= mask;
    }
}
void updateCol(int y, int digit){
    int mask = (1 << digit);
    for(int i = 1; i <= 9; i++){
        d[i][y].col |= mask;
    }
}
void updateGrid(int x, int y, int digit){
    int mask = (1 << digit);
    int gx = (x - 1) / 3 * 3 + 1;
    int gy = (y - 1) / 3 * 3 + 1;
    for(int i = gx; i < gx + 3; i++){
        for(int j = gy; j < gy + 3; j++){
         d[i][j].grid |= mask;
        }
    }
}
void reduceRow(int x, int digit){
    int mask = (1 << digit) ;
    for(int i = 1; i <= 9; i++){
        d[x][i].row ^= mask;
    }
}
void reduceCol(int y, int digit){
    int mask = (1 << digit);
    for(int i = 1; i <= 9; i++){
        d[i][y].col ^= mask;
    }
}
void reduceGrid(int x, int y, int digit){
    int mask = (1 << digit);
    int gx = (x - 1) / 3 * 3 + 1;
    int gy = (y - 1) / 3 * 3 + 1;
    for(int i = gx; i < gx + 3; i++){
        for(int j = gy; j < gy + 3; j++){
             d[i][j].grid ^= mask;
        }
    }
}
void dfs(int x,int y){
    //termination
    int cnt = 0;
    for(int i = 1; i <= 9; i++){
        cnt += (__builtin_popcount(d[i][i].row) == 9 
            && __builtin_popcount(d[i][i].col) == 9);
    }
    if(cnt == 9){
        output();
        exit(0);
    }
    //TODO
    int dx = 1, dy = 1, max = -(1<<30);
    for(int i = 1; i <= 9; i++){
        for(int j = 1; j <= 9; j++){
            if(c[i][j]) continue;
            int rowp = __builtin_popcount(d[i][j].row);
            int colp = __builtin_popcount(d[i][j].col);
            int gridp = __builtin_popcount(d[i][j].grid);
            if(max < rowp + colp + gridp){
                max = rowp + colp + gridp;
                dx = i, dy = j;
            }
        }
    }
    //enum
    for(int digit = 1; digit <= 9; digit++){
        int mask = (1 << digit);
        if(       d[dx][dy].row & mask
            || d[dx][dy].col & mask
            || d[dx][dy].grid & mask){
            continue;
        }
        updateRow(dx, digit);
        updateCol(dy, digit);
        updateGrid(dx, dy, digit);
        c[dx][dy] = digit;
        dfs(dx, dy);
        c[dx][dy] = 0;
        reduceRow(dx, digit);
        reduceCol(dy, digit);
        reduceGrid(dx, dy, digit);
    }
    
}
int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cerr.tie(nullptr);

    for(int i = 1; i <= 9; i++){
        for(int j = 1; j <= 9; j++){
            std::cin >> c[i][j];
            if(c[i][j]) {
                updateRow(i, c[i][j]);
                updateCol(j, c[i][j]);
                updateGrid(i, j, c[i][j]);
            }
        }
    }
    start = clock();

    dfs(1, 1);
    
    return 0;
}