POJ 3009 Curling 2.0(DFS深度优先搜索)

//DFS深度优先搜索，WA了5次就因为1个while后面的条件差了一个……教训啊！！！#include<iostream>using namespace std;int map[22][22],possible,minstep,w,h,beginx,beginy;void dfs(int x,int y,int r,int di)//di是4个方向的编号 1:向上 2：向右 3：向下 4：向左{if(r > minstep)return;//剪枝，超过最少步数的深搜无效返回if(di == 1){if(map[y-1][x] == -1||map[y-1][x] == 1)return;while(map[y-1][x] == 0||map[y-1][x] == 3){if(map[y-1][x] == 3){possible = 1;if(r < minstep)minstep = r;return;}y--;if(map[y-1][x] == -1)return;if(map[y-1][x] == 1){map[y-1][x] = 0;break;}}dfs(x,y,r+1,1);dfs(x,y,r+1,2);dfs(x,y,r+1,3);dfs(x,y,r+1,4);map[y-1][x] = 1;//很关键！一定要改回来！注意DFS的出口处恢复被修改过的值}else if(di == 2){if(map[y][x+1] == -1||map[y][x+1] == 1)return;while(map[y][x+1] == 0||map[y][x+1] == 3){if(map[y][x+1] == 3){possible = 1;if(r < minstep) minstep = r;return;}x++;if(map[y][x+1] == -1)return;if(map[y][x+1] == 1){map[y][x+1] = 0;break;}}dfs(x,y,r+1,1);dfs(x,y,r+1,2);dfs(x,y,r+1,3);dfs(x,y,r+1,4);map[y][x+1] = 1;} else if(di == 3){if(map[y+1][x] == -1||map[y+1][x] == 1)return;while(map[y+1][x] == 0||map[y+1][x] == 3){if(map[y+1][x] == 3){possible = 1;if(r < minstep) minstep = r;return;}y++;if(map[y+1][x] == -1)return;if(map[y+1][x] == 1){map[y+1][x] = 0;break;}}dfs(x,y,r+1,1);dfs(x,y,r+1,2);dfs(x,y,r+1,3);dfs(x,y,r+1,4);map[y+1][x] = 1;}else if(di == 4){if(map[y][x-1] == -1||map[y][x-1] == 1)return;while(map[y][x-1] == 0||map[y][x-1] == 3){if(map[y][x-1] == 3){possible = 1;if(r < minstep)minstep = r;return;}x--;if(map[y][x-1] == -1)return;if(map[y][x-1] == 1){map[y][x-1] = 0;break;}}dfs(x,y,r+1,1);dfs(x,y,r+1,2);dfs(x,y,r+1,3);dfs(x,y,r+1,4);map[y][x-1] = 1;} }int main(){while(cin >> w >> h){if(w == 0)break;memset(map,-1,sizeof(map));possible = 0;minstep = 10;for(int i = 1; i <= h;++i)for(int j = 1;j <= w;++j){cin >> map[i][j];if(map[i][j] == 2){map[i][j] = 0;beginx = j;beginy = i;}}//从起点开始向4个方向深搜dfs(beginx,beginy,1,1);dfs(beginx,beginy,1,2);dfs(beginx,beginy,1,3);dfs(beginx,beginy,1,4);if(possible)cout << minstep << endl;else cout << -1 << endl;}return 0;}