[JS] Find Peak Element

2022. 8. 5. 14:17

🔒 문제 (LeetCode 162)

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.

Constraints:

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

 

🌊 입출력

Example 1:

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:

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.

 


 

🔑 해결

🌌 알고리즘 - 이분탐색

/**
 * @param {number[]} nums
 * @return {number}
 */
var findPeakElement = function(nums) {
    let l = 0;
    let r = nums.length - 1;
    
    while(l < r) {
        let mid = l + r >>> 1;

        if(nums[mid] > nums[mid + 1]) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    
    return l;
};

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