Untitled

class Solution {
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& mat) {
        int m = mat.size() - 1;
        int n = mat[0].size() - 1;

        vector<vector<int>> ans(m + 1, vector<int>(n + 1));
        queue<pair<int, int>> bfs;

        for (int i = 0; i <= m; ++i)
        {
            for (int j = 0; j <= n; ++j)
            {
                if (mat[i][j] == 0)
                {
                    ans[i][j] = 0;
                    bfs.emplace(i, j);
                }
            }
        }
        
        while (bfs.size())
        {
            int i = bfs.front().first;
            int j = bfs.front().second;
            bfs.pop();
            
            if (i > 0 && mat[i -1][j])
            {
                mat[i - 1][j] = 0;
                ans[i - 1][j] = ans[i][j] + 1;
                bfs.emplace(i - 1, j);
            }
            if (i < m && mat[i + 1][j])
            {
                mat[i + 1][j] = 0;
                ans[i + 1][j] = ans[i][j] + 1;
                bfs.emplace(i + 1, j);
            }
            if (j > 0 && mat[i][j - 1])
            {
                mat[i][j - 1] = 0;
                ans[i][j - 1] = ans[i][j] + 1;
                bfs.emplace(i, j - 1);
            }
            if (j < n && mat[i][j + 1])
            {
                mat[i][j + 1] = 0;
                ans[i][j + 1] = ans[i][j] + 1;
                bfs.emplace(i, j + 1);
            }
        }
        
        return ans;
    }
};