1762 - Buildings With an Ocean View (Medium)
Problem Link
https://leetcode.com/problems/buildings-with-an-ocean-view/
Problem Statement
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 <= 10^51 <= heights[i] <= 10^9
Approach 1: Backwards
We iterate from right to left and track the maximum height. If the current building is taller than the maximum height, it means it has an ocean view and we can set it as the new max height.
Since we do it backwards, we reverse the answer at the end.
class Solution {
public:
vector<int> findBuildings(vector<int>& heights) {
int n = heights.size(), prev_mx = -1;
vector<int> ans;
// do it backwards
for (int i = n - 1; i >= 0; i--) {
// check if the current building is taller than the prev max
if (heights[i] > prev_mx) {
// if so, then this buildign has an ocean view
ans.push_back(i);
// update prev_mx
prev_mx = heights[i];
}
}
// reverse the order
reverse(ans.begin(), ans.end());
return ans;
}
};