Leetcode 162 Looking for peak value (June 11, 2022)

The peak element refers to the element whose value is strictly greater than the left and right adjacent values .

Give you an array of integers nums, Find the peak element and return its index . The array may contain multiple peaks , under these circumstances , return Any peak Just where you are .

You can assume nums[-1] = nums[n] = -∞ .

You must achieve a time complexity of O(log n) Algorithm to solve this problem .

Example 1：

Input ：nums = [1,2,3,1]
Output ：2
explain ：3 Is the peak element , Your function should return its index 2.
Example 2：

Input ：nums = [1,2,1,3,5,6,4]
Output ：1 or 5
explain ： Your function can return the index 1, Its peak element is 2;
Or return index 5, Its peak element is 6.

Tips ：

1 <= nums.length <= 1000
-231 <= nums[i] <= 231 - 1
For all that works i There are nums[i] != nums[i + 1]
Pass times 232,819 Submit the number 470,577

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/find-peak-element

Method 1 ： Two points search

C++ Submission ：

class Solution {
    
public:
    int findPeakElement(vector<int>& nums) {
    
        int n = nums.size();

        auto get = [=](int i) -> pair<int, int>{
    
            if(i == -1 || i == n){
    
                return {
    0, 0};
            }else{
    
                return {
    1, nums[i]};
            }
        };

        int l = 0, r = n, index = 0;
        while(l <= r){
    
            int mid = (l + r) / 2;
            if(get(mid - 1) < get(mid) && get(mid) > get(mid + 1)){
    
                index = mid;
                break;
            }
            if(get(mid) < get(mid + 1)){
    
                l = mid + 1;
            }else{
    
                r = mid - 1;
            }
        }
        return index;
    }
};