UVa 639 - Don't Get Rooked

/*回溯法*/#include <iostream>#include <cstring>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;const int MAX = 4+2;int board[MAX][MAX]; //棋盘int n;    // n*nint most; //输入时判断最大rooksint max_rooks; //最大rooks//判断当前位置是否可以插入int ok(int x, int y){    for(int i=y-1; i>=0; i--) {        if(board[x][i] == 2) return 0;        if(board[x][i] == 1) break;    }    for(int i=x-1; i>=0; i--) {        if(board[i][y] == 2) return 0;        if(board[i][y] == 1) break;    }    return 1;}//深度遍历，return 1：找到最大值了，直接返回int dfs(int x, int y, int rooks){    if(rooks==most) {max_rooks = rooks; return 1;}    if(x==n) {        if(rooks > max_rooks) max_rooks = rooks;        return 0;    }    int t_x, t_y; //下一步x、y坐标    if(y<n-1) {t_x = x; t_y = y+1;}    else {t_x = x+1; t_y=0;}    if(board[x][y] == 0 && ok(x, y)) {        board[x][y] = 2;        rooks++;        if(dfs(t_x, t_y, rooks)) return 1;        rooks--;        board[x][y] = 0;    }    if(dfs(t_x, t_y, rooks)) return 1;    return 0;}int main(void) {    #ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    #endif    while(scanf("%d", &n)==1 && n!=0) {        char ch;        max_rooks = 0;        most = 0;        getchar();        for(int i=0; i<n; i++) {            int found_dot = 0;            for(int j=0; j<n; j++) {                ch = getchar();                if(ch == '.') {                    if(!found_dot) {                        most++;                        found_dot = 1;                    }                    board[i][j] = 0;                } else if(ch=='X') {                    found_dot = 0;                    board[i][j] = 1;                }            }            while((ch=getchar()) != '\n');        }        dfs(0, 0, 0);        printf("%d\n", max_rooks);    }    return 0;}