[二分搜索] leetcode 162 Find Peak Element

problem:https://leetcode.com/problems/find-peak-element/

        根据下标二分搜索。每次检查mid左右两个数和mid的关系，决定如何进行下一步。

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        
        int n = nums.size();
        int low = 0;
        int high = n - 1;
       
        while(low <= high)
        {
       //     cout << low << " " << high << endl;
            int mid = (low + high) / 2;            
            int left = mid > 0 ? nums[mid - 1] : INT_MIN;
            int right = mid < n - 1 ? nums[mid + 1] : INT_MIN;
            
            if(left <= nums[mid] && right <= nums[mid])
            {
                return mid;
            }
            else if(left <= nums[mid] && nums[mid] <= right)
            {
                low = mid + 1;
            }
            else if(left >= nums[mid] && nums[mid] >= right)
            {
                high = mid - 1;
            }
            else
            {
                high = mid - 1;
            }
        }
        
        return 0;
    }
};