*** Error in `sandbox run': free(): invalid next size (fast): 0x000000000141f9d0 ***

class Solution {
private: 
    vector<int> d = {-1, 0, 1, 0, -1};
    int ans = 0;
    int n, m;
    
    struct Compare{
        bool operator() (vector<int> &a, vector<int> &b) {
            return a[0] < b[0];
        }
    }cmp;
    
public:
    int cutOffTree(vector<vector<int>>& forest) {
        int num_trees = 0;
        if (forest.size() == 0) return 0;
        if (forest[0][0] == 0) return -1;
        m = forest.size(); n = forest[0].size();
        vector<vector<int>> points;
        for(int i = 0; i < n; i++) 
            for(int j = 0; j < m; j++)
                if (forest[i][j] > 1) 
                    points.push_back({forest[i][j], i, j});
        sort(points.begin(), points.end(), cmp);
        if (forest[0][0] == 1)
            points.insert(points.begin(), {forest[0][0], 0, 0});
        for (int i = 0; i<points.size()-1; i++) {
            int t = bfs(forest, points[i], points[i+1]);
            if (t == -1) return -1;
            ans += t;
        }
        return ans;
    }
    
    int bfs(vector<vector<int>>& forest, vector<int> src, vector<int> dst) {
        vector<vector<int>> vst(m, vector<int>(n, 0));
        queue<vector<int>> q;
        q.push({src[1], src[2]});
        vst[src[1]][src[2]] = 1;
        while(!q.empty()) {
            auto top = q.front();
            q.pop();
            if (top[0] == dst[1] && top[1] == dst[2]) 
                return vst[top[0]][top[1]] - 1;
            for (int i = 0; i<4; i++) {
                int x = top[0] + d[i], y = top[1] + d[i+1];
                if (isvalid(x, y) && forest[x][y] && !vst[x][y]) {
                    q.push({x, y});
                    vst[x][y] = vst[top[0]][top[1]] + 1;
                }
            }
        }
        return -1;
    }
    
    bool isvalid(int x, int y) {
        return x >= 0 && x < m && y >= 0 && y < n;
    }
};