Number of Visible People in Queue — Monotonic Stack

# Python
def canSeePersonsCount(heights):
    n = len(heights); ans = [0]*n; stack = []
    for i in range(n-1, -1, -1):
        count = 0
        while stack and stack[-1] < heights[i]:
            stack.pop(); count += 1
        if stack: count += 1  # see the blocking taller person
        ans[i] = count
        stack.append(heights[i])
    return ans

// Java
public int[] canSeePersonsCount(int[] heights) {
    int n=heights.length; int[] ans=new int[n]; Deque<Integer> stack=new ArrayDeque<>();
    for (int i=n-1;i>=0;i--) {
        int count=0;
        while (!stack.isEmpty() && stack.peek()<heights[i]) { stack.pop(); count++; }
        if (!stack.isEmpty()) count++;
        ans[i]=count; stack.push(heights[i]);
    }
    return ans;
}