leetcode - 1762. Buildings With an Ocean View

Description

There are n buildings in a line. You are given an integer array heights of size n that represents the heights of the buildings in the line.

The ocean is to the right of the buildings. A building has an ocean view if the building can see the ocean without obstructions. Formally, a building has an ocean view if all the buildings to its right have a smaller height.

Return a list of indices (0-indexed) of buildings that have an ocean view, sorted in increasing order.

Example 1:

Input: heights = [4,2,3,1]
Output: [0,2,3]
Explanation: Building 1 (0-indexed) does not have an ocean view because building 2 is taller.

Example 2:

Input: heights = [4,3,2,1]
Output: [0,1,2,3]
Explanation: All the buildings have an ocean view.

Example 3:

Input: heights = [1,3,2,4]
Output: [3]
Explanation: Only building 3 has an ocean view.

Constraints:

1 <= heights.length <= 10^5
1 <= heights[i] <= 10^9

Solution

Iterate from right to left, only push those taller than top element into the stack.

Time complexity: $o(n)$
Space complexity: $o(n)$

Code

class Solution:
    def findBuildings(self, heights: List[int]) -> List[int]:
        stack = []
        for i in range(len(heights) - 1, -1, -1):
            if not stack or heights[stack[-1]] < heights[i]:
                stack.append(i)
        return stack[::-1]