找了半天，锁定bug是find()返回-1，传到tmin的参数f里面突然就变成了0？？？我好懵啊……大佬们解释一下（可以去IDE看看他都干了啥，可以采用输出调试法锁定错误） 《真·爆零》

#include <bits/stdc++.h>
using namespace std;

int t;
string str;

struct loc
{
    int x;
    int y;
    int dis(loc that)
    {
        return abs(this -> x - that.x) + abs(this -> y - that.y);
    }
    loc & move(char mov)
    {
        if (mov == 'E')
        {
            this -> y--;
            return * this;
        }
        if (mov == 'S')
        {
            this -> x--;
            return * this;
        }
        if (mov == 'W')
        {
            this -> y++;
            return * this;
        }
        if (mov == 'N')
        {
            this -> x++;
            return * this;
        }
    }
}a, b;

int tmin(int f, int s)
{
    if (f == -1) return s;
    if (s == -1) return f;
    return min(f, s);
}

int find(loc x, loc y, int tim)
{
    if (x.dis(y) > tim) return -1;
    if (x.dis(y) == 0) return 0;
    return tmin(find(x, y, tim - 1), find(x.move(str.at(t - tim)), y, tim - 1) + 1);
}

int main()
{
    cin >> a.x >> a.y >> b.x >> b.y >> t;
    for (int i = 1; i <= t; i++)
    {
        char ch;
        cin >> ch;
        str += ch;
    }
    cout << find(a, b, t) << endl;
    return 0;
}