LeetCode Challenge #162. Find Peak Element

Day 25 of 100 Days LeetCode Challenge

Question 55 of 75 - LeetCode Weekly Challenge

LeetCode Challenge #162. Find Peak Element

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

Given a 0-indexed integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

You may imagine that nums[-1] = nums[n] = -∞. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.

You must write an algorithm that runs in O(log n) time.

Example 1:

Input: nums = [1,2,3,1]
Output: 2
Explanation: 3 is a peak element and your function should return the index number 2.

Example 2:

Input: nums = [1,2,1,3,5,6,4]
Output: 5
Explanation: Your function can return either index number 1 where the peak element is 2, or index number 5 where the peak element is 6.

Constraints:

1 <= nums.length <= 1000
-2³¹ <= nums[i] <= 2³¹ - 1
nums[i] != nums[i + 1] for all valid i.

Java Video Solution

C++ Video Solution

Java Solution

				
					class Solution {
    public int findPeakElement(int[] nums) {
        if(nums.length==1){
            return 0;
        }else if ( nums[0]>nums[1]){
            return 0;
        }else if ( nums[nums.length-1]>nums[nums.length-2]){
            return nums.length-1;
        }else {
            int start = 1 ;
            int end = nums.length-2;
            while(start<=end){
                 int mid = ( start + end)/2;
                 if(nums[mid]>nums[mid-1] && nums[mid]>nums[mid+1]){
                     return mid ;
                 }else if ( nums[mid]<nums[mid+1]){
                     start = mid+1 ;
                 }else{
                     end = mid-1 ;
                 }
             }
           return -1 ;  
        }
    }
}

C++ Solution

				
					class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        int end=nums.size()-1;
        int start=0;
        int mid=start+ (end-start)/2;

        while(start<end)
        {
            mid= start + (end-start)/2;
            if(nums[mid]>nums[mid+1])end=mid;
            else start=mid+1;
        }
        return end;
    }
};

Day 25 of 100 Days LeetCode Challenge

Question 55 of 75 - LeetCode Weekly Challenge