【HDOJ】1045 Fire Net

经典深搜。注意满足条件。

#include <stdio.h>
#include <string.h>

#define MAXNUM 5

char map[MAXNUM][MAXNUM];
int visit[MAXNUM][MAXNUM];

int chk(int row, int col, int n) {
    int i, k;

    if (row<0 || row>=n || col<0 || col>=n )
        return 0;
    if (visit[row][col] || map[row][col]!='.')
        return 0;

    // if this position is valid or not
    k = 0;
    for (i=col-1; i>=0; --i) {
        if (map[row][i] == 'X')
            break;
        if (map[row][i] == '.' && visit[row][i]) {
            k = 1;
            break;
        }
    }
    if (k) return 0;

    for (i=col+1; i<n; ++i) {
        if (map[row][i] == 'X')
            break;
        if (map[row][i] == '.' && visit[row][i]) {
            k = 1;
            break;
        }
    }
    if (k) return 0;

    for (i=row-1; i>=0; --i) {
        if (map[i][col] == 'X')
            break;
        if (map[i][col] == '.' && visit[i][col]) {
            k = 1;
            break;
        }
    }
    if (k) return 0;

    for (i=row+1; i<n; ++i) {
        if (map[i][col] == 'X')
            break;
        if (map[i][col] == '.' && visit[i][col]) {
            k = 1;
            break;
        }
    }

    if (k)
        return 0;
    else
        return 1;
}

int dfs(int n) {
    int i, j, tmp, max = 0;

    for (i=0; i<n; ++i) {
        for (j=0; j<n; ++j) {
            if ( chk(i, j, n) ) {
                visit[i][j] = 1;
                tmp = dfs(n) + 1;
                if (tmp > max)
                    max = tmp;
                visit[i][j] = 0;
            }
        }
    }

    return max;
}

int main() {
    int n, amount;
    int i;

    while (scanf("%d", &n)!=EOF && n) {
        getchar();
        for (i=0; i<n; ++i)
            gets(map[i]);

        memset(visit, 0, sizeof(visit));
        amount = dfs(n);
        printf("%d
", amount);
    }

    return 0;
}