LeetCode 1944: Number of Visible People in a Queue Solution

Master LeetCode problem 1944 (Number of Visible People in a Queue), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1944. Number of Visible People in a Queue

Hard

Array Stack Monotonic Stack

Problem Explanation

Explanation:

To solve this problem, we can use a monotonic decreasing stack to keep track of the visible people in the queue. We iterate through the queue from right to left and maintain a stack of indices. For each person, we pop elements from the stack until we find a person taller than the current person or the stack becomes empty. The number of visible people for the current person is the difference between the current index and the top of the stack. Finally, we push the current index onto the stack.

Time Complexity: O(n) where n is the number of people in the queue. Space Complexity: O(n) where n is the number of people in the queue.

Solution Code

class Solution {
    public int[] canSeePersonsCount(int[] heights) {
        int n = heights.length;
        int[] result = new int[n];
        Stack<Integer> stack = new Stack<>();
        
        for (int i = n - 1; i >= 0; i--) {
            while (!stack.isEmpty() && heights[i] > heights[stack.peek()]) {
                result[i] += 1 + result[stack.pop()];
            }
            if (!stack.isEmpty()) {
                result[i]++;
            }
            stack.push(i);
        }
        
        return result;
    }
}

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