Leetcode 162. Find Peak Element

文章作者：Tyan
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1. Description

Find Peak Element

2. Solution

• Version 1

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

• Version 2

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

• Version 3

class Solution {
public:
    int findPeakElement(vector& nums) {
        int left = 0;
        int 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;
    }
};

• Version 4

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

Reference

1. https://leetcode.com/problems/find-peak-element/description/