162. Find Peak Element, 자바 풀이

[문제]
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:
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.

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

https://leetcode.com/problems/find-peak-element/description/?envType=study-plan-v2&envId=top-interview-150

class Solution {
    public int findPeakElement(int[] nums) {
        int l = 0;
        int r = nums.length - 1;
        int mid = 0;

        while (l < r) {
            mid = (l + r) / 2;

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

        return r;
    }
}

// 이분탐색을 활용한다.
// 중간값이 mid + 1 의 값 보다 작다면
// left = mid + 1

// mid + 1 의 값 보다 크다면
// right = mid - 1

// 결국 mid 값이 mid + 1 보다 큰 마지막의 경우가 가장 큰 수이다.