class Solution {
public:
    int maxDistance(vector<vector<int>>& grid) {
        vector<pair<int,int>>wa,la;
        int n=size(grid);
        for(int i=0;i<n;i++)for(int j=0;j<n;j++)
            if(grid[i][j])la.emplace_back(i,j);else wa.emplace_back(i,j);
        if(wa.empty()||la.empty())return -1;
        int r=0;
        for(auto&[i,j]:wa)
        {
            int m=1e9;
            for(auto&[x,y]:la)m=min(m,abs(i-x)+abs(j-y));
            r=max(r,m);
        }
        return r;
    }
};