Buildings With an Ocean View

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.

思路：就是个单调栈，4,2,3,那么2就没有必要存了，因为小于3，那么栈里面就是个单调递减的。

class Solution {
    public int[] findBuildings(int[] heights) {
        Stack stack = new Stack<>();
        for(int i = 0; i < heights.length; i++) {
           while(!stack.isEmpty() && heights[stack.peek()] <= heights[i]) {
               stack.pop();
           }
           stack.push(i);
        }
        int[] res = new int[stack.size()];
        int j = res.length - 1;
        while(!stack.isEmpty()) {
            res[j] = stack.pop();
            j--;
        }
        return res;
    }
}