Problem

Given a mountain sequence of n integers which increase firstly and then decrease, find the mountain top.

Example
Given nums = [1, 2, 4, 8, 6, 3] return 8
Given nums = [10, 9, 8, 7], return 10

思路

1. 暴力for 循环
2. 二分法
   1. 找到中点mid
   2. [mid - 1], [mid] 和 [mid + 1] 作比较

    public int mountainSequence(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }

        int start = 0;
        int end = nums.length - 1;

        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (nums[mid - 1] < nums[mid] && nums[mid] > nums[mid + 1]) {
                return nums[mid];
            }
            if (nums[mid - 1] <= nums[mid] && nums[mid] <= nums[mid + 1]) {
                start = mid;
            } else {
                end = mid;
            }
        }

        if (nums[start] > nums[end]) {
            return nums[start];
        }
        return nums[end];
    }