int solution(vector<vector<int>>&; apples, int m, int n, int k){ vector<vector<int>> tree_heights(n); for (int i = 0; i < m; i++) { tree_heights[apples[i][0]-1].push_back(apples[i][1]); } int res = 0; for (int i = 0; i < n; i++) { sort(tree_heights[i].begin(), tree_heights[i].end()); int max_cnt = INT_MIN; for (int j = 0; j < tree_heights[i].size(); j++) { int upper = tree_heights[i][j] + k; int cnt = 1, start = j + 1; while (start < tree_heights[i].size() &;&; tree_heights[i][start] <= upper) { cnt++; start++; } max_cnt = max(max_cnt, cnt); } res += max_cnt; } return res; }