Leetcode Find Peak Element 162

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.

题目链接

解法一：

class Solution {public:    int findPeakElement(vector<int>& nums) {        int len = nums.size();        if (len == 1) return 0;        else if(len == 2) return nums[0]>nums[1] ? 0 : 1;        else{             int ans = 0;             if (nums[0] > nums[1]) return 0;             for(int i = 1; i <= len - 2; i++){                 if (nums[i] > nums[i-1] && nums[i] > nums[i+1]){                     ans = i;                     break;                 }             }             if(nums[len - 1] > nums[len - 2]) return len - 1;             return ans;        }    }};

hint提示二分查找：

class Solution {public:    int findPeakElement(vector<int>& nums) {        int len = nums.size();        unsigned left = 0, right = len - 1 , mid;        while(left <= right){            if(left == right) break;            mid = (left + right)/2;            if (nums[mid] < nums[mid + 1]) {                left = mid + 1;            }else {                right = mid;             }        }        return left;    }};