LeetCode 1944. Number of Visible People in a Queue

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class Solution {
public:
    vector<int> canSeePersonsCount(vector<int>& heights) {
        int n = heights.size();
        vector<int> ans(n);
        stack<int> stk;
        for (int i = 0; i < n; ++i) {
            int h = heights[i];
            while (!stk.empty() && heights[stk.top()] <= h)
                ++ans[stk.top()], stk.pop();
            if (!stk.empty())
                ++ans[stk.top()];
            stk.emplace(i);
        }
        return ans;
    }
};