HDU 1728

http://acm.hdu.edu.cn/showproblem.php?pid=1728

要注意题目给的输入顺序，

dfs里面第三条如果不共线并且相应步数已经到了的话

#include <bits/stdc++.h>
using namespace std;
int t,m,n,k,x1,yy1,x2,y2;
char mp[110][110];
int turn[110][110];
int flag;
int dx[4] = {0,0,-1,1};
int dy[4] = {-1,1,0,0};
void dfs(int x,int y,int dir){
    if(x == x2  && y == y2 && turn[x][y] <= k){
        flag = 1;
        return;
    }
    if(turn[x][y] > k)
        return;
    if(x != x2 && y != y2 && turn[x][y] == k)
        return;
    for(int i = 0; i < 4; i++){
        int xx = x + dx[i];
        int yy = y + dy[i];
        if(xx <= 0 ||xx > m || yy <= 0 || yy > n || mp[xx][yy] == '*')
            continue;
        //xx yy 已经走过了，并且上次走的要比这次小
        if(turn[xx][yy] < turn[x][y])
            continue;
        //需要转弯，并且转弯之后还小，说明之前走过
        if(dir != -1 && i != dir && turn[xx][yy] < turn[x][y] + 1)
            continue;
        if(dir != -1 && i != dir)
            turn[xx][yy] = turn[x][y] + 1;
        else turn[xx][yy] = turn[x][y];
        mp[xx][yy] = '*';
        dfs(xx,yy,i);
        mp[xx][yy] = '.';
        if(flag) return;
    }
}
int main(){
    //freopen("in","r",stdin);
    ios::sync_with_stdio(0);
    cin >> t;
    while(t--){
        cin >> m >> n;
        for(int i = 1; i <= m; i++){
            for(int j = 1; j <= n; j++)
                cin >> mp[i][j];
        }
        cin >> k >> yy1 >> x1 >> y2 >> x2;
        memset(turn,0x3f, sizeof(turn));
        flag = 0;
        turn[x1][yy1] = 0;
        dfs(x1,yy1,-1);
        if(flag) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}