162. 寻找峰值

162. 寻找峰值

 https://leetcode.cn/problems/find-peak-element/description/

 

思路

https://leetcode.cn/problems/find-peak-element/solutions/998152/xun-zhao-feng-zhi-by-leetcode-solution-96sj/

 

Code

二分查找法。需要对 两个端点做特殊处理。

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        int n = nums.size();
        
        if (n == 1){
            return 0;
        }

        int left = 0;
        int right = n-1;

        int ans = -1;
        while(left<=right){
            int middle = (left+right) / 2;

            if (middle == 0){
                if (nums[middle] < nums[middle+1]){
                    ans = middle+1;
                } else {
                    ans = middle;
                }
                
                break;
            } else if (middle == n-1){
                if (nums[middle] > nums[middle-1]){
                    ans = middle;
                } else {
                    ans = middle-1;
                }
                
                break;                
            }

            if (nums[middle] > nums[middle+1] && nums[middle] > nums[middle-1]){
                ans = middle;
                break;
            }

            if (nums[middle] < nums[middle+1]){
                left = middle+1;
            }else{
                right = middle-1;
            }
        }

        return ans;
    }
};