C Exercises: Find the index of first peak element in a given array

Last update on August 01 2025 13:00:04 (UTC/GMT +8 hours)

97. Index of First Peak Element

Write a program in C to find the index of the first peak element in a given array.

Expected Output:
The given array is:
5 12 13 20 16 19 11 7 25
The index of first peak element in the array is: 3

The task is to write a C program that finds the index of the first peak element in a given array. A peak element is defined as an element that is greater than its neighbors. The program should traverse the array, identify the first occurrence of such an element, and display its index.

Sample Solution:

C Code:

#include<stdio.h>

// Function to search for a peak element recursively
int peakElementSearch(int arr1[], int ele_low, int ele_high, int n) 
{ 
    int ele_mid = ele_low + (ele_high - ele_low) / 2;  

    // Check if the element at mid is a peak or not
    if ((ele_mid == 0 || arr1[ele_mid - 1] <= arr1[ele_mid]) &&
        (ele_mid == n - 1 || arr1[ele_mid + 1] <= arr1[ele_mid])) 
        return ele_mid; 
    else if (ele_mid > 0 && arr1[ele_mid - 1] > arr1[ele_mid]) 
        return peakElementSearch(arr1, ele_low, (ele_mid - 1), n); 
    else 
        return peakElementSearch(arr1, (ele_mid + 1), ele_high, n); 
} 

// Function to find a peak element in an array
int PeakFinding(int arr1[], int n) 
{ 
    return peakElementSearch(arr1, 0, n - 1, n); 
} 

int main() 
{ 
    int arr1[] = {5, 12, 13, 20, 16, 19, 11, 7, 25}; 
    int n = sizeof(arr1) / sizeof(arr1[0]);
    int i = 0; 

    // Print the original array
    printf("The given array is:  \n");
    for (i = 0; i < n; i++)
    {
        printf("%d  ", arr1[i]);
    }
    printf("\n");

    // Find the index of the first peak element in the array
    printf("The index of the first peak element in the array is: %d", PeakFinding(arr1, n)); 
    return 0; 
}

Output:

The given array is:  
5  12  13  20  16  19  11  7  25  
The index of first peak element in the array is: 3

Visual Presentation:

Flowchart:/p>

For more Practice: Solve these Related Problems:

• Write a C program to find the first peak element in an array by comparing each element with its neighbors.
• Write a C program to identify the index of the first peak using a binary search approach in a unimodal array.
• Write a C program to determine the first peak element recursively.
• Write a C program to find the first peak and then output both the peak value and its index.

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