【HDOJ】1010 Tempter of the Bone

经典搜索+剪枝，这还是第一次知道什么是剪枝，主要还是奇偶剪枝，这题非常经典。

#include <iostream>
#include <cstdio>
using namespace std;

#define MAXNUM 10

int n, m, t;
char maze[MAXNUM][MAXNUM];
// upper, lower, left and right
int direction[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
int si, sj, di, dj;
bool survive;

void dfs(int si, int sj, int cnt) {
    int tmp1, tmp2;

    if (cnt==t && si==di && sj==dj) {
        survive = true;
        return ;
    }

    tmp1 = abs(si-di)+abs(sj-dj);
    if ( t-cnt < tmp1 )
        return ;
    if ( (t-cnt-tmp1)%2 != 0)
        return ;

    for (int i=0; i<4; ++i) {
        tmp1 = si + direction[i][0];
        tmp2 = sj + direction[i][1];
        if (tmp1 && tmp2 && tmp1<=n && tmp2<=m && maze[tmp1][tmp2] != 'X') {
            maze[tmp1][tmp2] = 'X';
            dfs(tmp1, tmp2, cnt+1);
            if ( survive )
                return ;
            maze[tmp1][tmp2] = '.';
        }
    }
}

int main() {
    int i, j;
    int wall;

    while (cin>>n>>m>>t) {
        if (n==0 && m==0 && t==0)
            break;

        wall = 0;
        for (i=1; i<=n; ++i) {
            for (j=1; j<=m; ++j) {
                cin >>maze[i][j];
                if (maze[i][j] == 'S') {
                    si = i;
                    sj = j;
                }
                if (maze[i][j] == 'D') {
                    di = i;
                    dj = j;
                }
                if (maze[i][j] == 'X')
                    wall++;
            }
        }

        if (n*m-wall < t) {
            printf("NO\n");
        } else {
            survive = false;
            maze[si][sj] = 'X';
            dfs(si, sj, 0);
            if (survive)
                printf("YES\n");
            else
                printf("NO\n");
        }
    }

    return 0;
}