矩阵距离
多点BFS

#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
int d[N][N], g[N][N];

int main()
{
    queue<pair<int,int>> q;
    int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
    memset(d,0x3f, sizeof d);
    int n, m;
    cin >> n >> m;
    for (int i = 0 ; i < n ; i ++ ) {
        string s;
        cin >> s;
        for (int j = 0 ; s[j] ; j ++ ) {
            if (s[j] == '1') {
                q.push({i, j});
                d[i][j] = 0;
            }
        }
    }

    while (q.size()) {
        int l = q.size();
        for (int i = 0 ; i < l ; i ++ ) {
            auto t = q.front();
            q.pop();
            for (int j = 0 ; j < 4 ; j ++ ) {
                int x = t.first + dx[j];
                int y = t.second + dy[j];
                if (x >= 0 && x < n && y >= 0 && y < m && d[x][y] == 0x3f3f3f3f) {
                    q.push({x, y});
                    d[x][y] = min(d[x][y], d[t.first][t.second] + 1);
                }
            }
        }
    }

    for (int i = 0 ; i < n ; i ++ ) {
        for (int j = 0 ; j < m ; j ++ ) cout << d[i][j] << ' ';
        cout << endl;
    }
    return 0;
}