参考答案：

#include<iostream>
#include<queue>
#include<cstring>

using namespace std;

typedef pair<int, int>PII;
const int N = 1010;
int g[N][N], f[N][N];
int n, m;

void bfs(int a, int b)
{
    queue<PII> q;
    q.push({ a,b });
    g[a][b] = 1;

    while (q.size())
    {
        PII t = q.front();
        q.pop();
        int dx[4] = { 0,0,-1,1 }, dy[4] = { 1,-1,0,0 };
        for (int i = 0; i < 4; ++i)
        {
            int x = t.first + dx[i], y = t.second + dy[i];
            if (g[x][y] == 0)
            {
                g[x][y] = 1;
                f[x][y] = f[t.first][t.second] + 1;
                q.push({ x,y });
            }
        }
    }

    cout << f[n][m] << endl;
}
int main()
{
    memset(g, 1, sizeof(g));
    cin >> n >> m;

    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            cin >> g[i][j];

    bfs(1, 1);

    return 0;
}