群里有个jk大佬贴的代码，用距离做的剪枝，记录下来学习一下

#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;

int n, m;

const int N = 110;

int g[N][N];
int ans = N * N;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int st[N][N];

void dfs(int x, int y, int cnt)
{
    if(cnt > ans) return;
    if(x == n - 1 && y == m - 1)
    {
        ans = cnt;
        return;
    }

    for(int i = 0; i < 4; i ++)
    {
        int newX = x + dx[i];
        int newY = y + dy[i];
        if(newX >= 0 && newY >= 0 && newX < n && newY < m && g[newX][newY] == 0 && st[newX][newY] > st[x][y] + 1)
        {
            st[newX][newY] = st[x][y] + 1;
            dfs(newX, newY, cnt + 1);
        }
    }
}

int main()
{
    scanf("%d%d", &n, &m);
    for(int i = 0; i < n; i ++)
        for(int j = 0; j < m; j ++)
            scanf("%d", &g[i][j]);

    memset(st, 0x3f, sizeof st);
    st[0][0] = 0;
    dfs(0, 0, 0);
    cout << ans << endl;
    return 0;
}