162. Find Peak Element

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162. Find Peak Element

Description

Difficulty: Medium

Related Topics: Array, Binary Search

A peak element is an element that is strictly greater than its neighbors.

Given a 0-indexed integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

You may imagine that nums[-1] = nums[n] = -∞. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.

You must write an algorithm that runs in O(log n) time.

Example 1:

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Input: nums = [1,2,3,1]
Output: 2
Explanation: 3 is a peak element and your function should return the index number 2.

Example 2:

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Input: nums = [1,2,1,3,5,6,4]
Output: 5
Explanation: Your function can return either index number 1 where the peak element is 2, or index number 5 where the peak element is 6.

Constraints:

  • 1 <= nums.length <= 1000
  • -231 <= nums[i] <= 231 - 1
  • nums[i] != nums[i + 1] for all valid i.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        int left = -1, right = nums.size() - 1;
        while (left + 1 < right) {
            int mid = (right - left) / 2 + left;
            if (nums[mid] < nums[mid + 1]) {
                left = mid;
            } else {
                right = mid;
            }
        }
        return right;
    }
};