LeetCode 峰值

162. 寻找峰值

题目描述：

解法一（迭代）：

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

解法二（递归）：

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

852. 山脉数组的峰顶索引

题目描述：

解法一：

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& A) {
        return max_element(A.begin(),A.end())-A.begin();
    }
};

解法二：

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