C++ Program to Find Largest Element in an Array

Given an array arr of size N, the task is to find the largest element in the given array. 

Example:

Input: arr[] = {10, 20, 4}
Output: 20

Input : arr[] = {20, 10, 20, 4, 100}
Output : 100

Approach 1 – Linear Traversal: One of the most simplest and basic approach to solve this problem is to simply traverse the whole list and find the maximum among them. 

Follow the steps below to implement this idea:

• Create a local variable max to store the maximum among the list
• Initialize max with the first element initially, to start the comparison.
• Then traverse the given array from second element till end, and for each element:
  • Compare the current element with max
  • If the current element is greater than max, then replace the value of max with the current element.
• At the end, return and print the value of the largest element of array stored in max.

Below is the implementation of the above approach: 

CPP

// C++ program to find maximum
// in arr[] of size n
#include <bits/stdc++.h>
using namespace std;

int largest(int arr[], int n)
{
    int i;

    // Initialize maximum element
    int max = arr[0];

    // Traverse array elements
    // from second and compare
    // every element with current max
    for (i = 1; i < n; i++)
        if (arr[i] > max)
            max = arr[i];

    return max;
}

// Driver Code
int main()
{
    int arr[] = {10, 324, 45, 90, 9808};
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << "Largest in given array is " <<
             largest(arr, n);
    return 0;
}

// This Code is contributed by Shivi_Aggarwal

Output:

Largest in given array is 9808

Time complexity: O(N), to traverse the Array completely.
Auxiliary Space: O(1), as only an extra variable is created, which will take O(1) space.

Approach 2: Using Library Function: Most of the languages have a relevant max() type in-built function to find the maximum element, such as  std::max_element in C++. We can use this function to directly find the maximum element. 

Below is the implementation of the above approach: 

C++

// C++ program to find maximum
// in arr[] of size n
#include <bits/stdc++.h>
using namespace std;

// Returns maximum in arr[]
// of size n
int largest(int arr[], int n)
{
    return *max_element(arr, arr+n);
}

// Driver code
int main()
{
    int arr[] = {10, 324, 45, 90, 9808};
    int n = sizeof(arr)/sizeof(arr[0]);
    cout << largest(arr, n);
    return 0;
}

Output

9808

Time complexity: O(N), since the in-built max_element() function takes O(N) time.
Auxiliary Space: O(1), as only an extra variable is created, which will take O(1) space.

Approach 3: Using Recursion: we will call recursive function for finding maximum elements in index  from 1 to n-1 and then call recursive function for finding maximum elements in index from 2 to n-1 and so on and return maximum element every time.

Below is the implementation of the above approach: 

C++

// C++ implementation of the above approach

#include <bits/stdc++.h>
using namespace std;

// Function to largest element using Recursion
int largest(int *arr , int n , int i)
{
    //Base case
    if (i == n-1) // if we reach last element of the array
    {             // return value of that index
        return arr[i];
    }

    // recursive call for find maximum element
    return max( arr[i] ,largest( arr , n , i+1) );
    // it will return maximum of arr[i] and arr[i+1] to arr[n-1]
}

// Drive Code
int main()
{
    int arr[] = {10, 324, 45, 90, 9808};
    int n = sizeof(arr)/sizeof(arr[0]);

    // Function call
    cout << largest(arr, n , 0);

    return 0;
}

// This Approach is contributed by nikhilsainiofficial546

Output

9808

Time complexity: O(N)
Auxiliary Space: O(N ), because of recursive call 

Approach 4(Using sort funciton):

This approach to solve the problem is to sort the array in increasing order using sort stl and then return the last element of the array which will be the largest.

Algorithm:

1.    Define a function named largest which takes an integer array arr and its size n as input.
2.    Sort the array arr in increasing order using the sort function in C++.
3.    Return the (n-1)th element of the sorted array which will be the largest element in the array.
4.    In the main function, define an integer array arr and its size n, and assign some values to the array.
5.    Call the largest function with the array arr and size n as inputs and print its return value.

Below is the implementation of the approach:

C++

// C++ implementation of the above approach

#include <bits/stdc++.h>
using namespace std;

// Function to find largest element
int largest(int *arr, int n) {
    // Sort the array in
      // increasing order
    sort(arr, arr + n);

      // return the (n-1)th element
      return arr[n-1];
}

// Driver's Code
int main() {
    int arr[] = {10, 324, 45, 90, 9808};
    int n = sizeof(arr)/sizeof(arr[0]);

    // Function call
    cout << largest(arr, n);

    return 0;
}

Output

9808

Time Complexity: O(N * log₂N) as sort function has been called which takes N*log₂N time. Here, N is size of input array.

Auxiliary Space: O(1) as no extra space has been used.