How hard is LeetCode 2345. Finding the Number of Visible Mountains?

LeetCode 2345. Finding the Number of Visible Mountains is rated Medium on LeetCode.

What is the time complexity of LeetCode 2345. Finding the Number of Visible Mountains?

The Python solution on this page runs in O(n \times \log n).

What is the space complexity of LeetCode 2345. Finding the Number of Visible Mountains?

The Python solution on this page uses O(n) auxiliary space.

What topics does LeetCode 2345. Finding the Number of Visible Mountains cover?

LeetCode 2345. Finding the Number of Visible Mountains is tagged Stack, Array, Sorting and Monotonic Stack on LeetCode.

Is LeetCode 2345. Finding the Number of Visible Mountains a premium problem?

Yes. LeetCode 2345. Finding the Number of Visible Mountains is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.

Finding the Number of Visible Mountains — LeetCode 2345 Python Solution

MediumLeetCode PremiumStackArraySortingMonotonic Stack

Problem: #2345
Pattern: Stack
Reading time: 3 min
Source: leetcode.com

The problem

You are given a 0-indexed 2D integer array peaks where peaks[i] = [xi, yi] states that mountain i has a peak at coordinates (xi, yi). A mountain can be described as a right-angled isosceles triangle, with its base along the x-axis and a right angle at its peak.

Example

Input: peaks = [[2,2],[6,3],[5,4]]
Output: 2
Explanation: The diagram above shows the mountains.

Python solution

Python

class Solution:
    def visibleMountains(self, peaks: List[List[int]]) -> int:
        arr = [(x - y, x + y) for x, y in peaks]
        cnt = Counter(arr)
        arr.sort(key=lambda x: (x[0], -x[1]))
        ans, cur = 0, -inf
        for l, r in arr:
            if r <= cur:
                continue
            cur = r
            if cnt[(l, r)] == 1:
                ans += 1
        return ans

Complexity

Measure	Complexity
Time	O(n \times \log n)
Space	O(n) auxiliary

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 2345. Finding the Number of Visible Mountains is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 2345. Finding the Number of Visible Mountains?: LeetCode 2345. Finding the Number of Visible Mountains is rated Medium on LeetCode.
What is the time complexity of LeetCode 2345. Finding the Number of Visible Mountains?: The Python solution on this page runs in O(n \times \log n).
What is the space complexity of LeetCode 2345. Finding the Number of Visible Mountains?: The Python solution on this page uses O(n) auxiliary space.
What topics does LeetCode 2345. Finding the Number of Visible Mountains cover?: LeetCode 2345. Finding the Number of Visible Mountains is tagged Stack, Array, Sorting and Monotonic Stack on LeetCode.
Is LeetCode 2345. Finding the Number of Visible Mountains a premium problem?: Yes. LeetCode 2345. Finding the Number of Visible Mountains is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.