Leetcode 852. Peak Index in a Mountain Array

アプローチ1

Brute-force

class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int before = 0;
        for (int i = 0; i < arr.length; i++) {
            if (before <= arr[i]) {
                before = arr[i];
                continue;
            }
            return i - 1;
        }
        return before;
    }
}

アプローチ2

二分探索

class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 0;
        int right = arr.length - 1;

        while (left < right) {
            int mid = (left + right) / 2;

            if (arr[mid] < arr[mid + 1]) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }
        return left;
    }
}