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C Program to find second largest element of an array.

C Code Example — Array Programs

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C Program to find second largest element of an array.

Objective

Write a C program to find the second largest element of an array.

Algorithm / Approach

  1. Read an array of size n.
  2. Find the absolute largest element (max) and record its index j.
  3. Initialize the second largest smax to an element at the opposite end of the array.
  4. Loop through the array again to find the maximum value, but skip the index j using the condition j != i.
  5. Print the second largest element.
main.c 
#include<stdio.h>
int main() {
 int a[50],n,i,j=0,max,smax;
 printf("Enter Array Size: ");
 scanf("%d",&n);
 printf("Enter %d element: ",n);
 for(i=0;i< n;i++)
  scanf("%d",&a[i]);
 max=a[0];
 for(i=1;i< n;i++) {
  if(max < a[i]) {
   max=a[i];
   j = i;
  }
 }
 smax=a[n-j-1];
 for(i=1;i< n;i++) {
  if(smax < a[i] && j != i)
   smax = a[i];
 }
 printf("2nd Largest: %d",smax);
 return 0;
}

Expected Output

Enter Array Size: 5
Enter 5 element: 1 2 3 4 5
2nd Largest: 4

Explanation of the Program

  • Just like finding the second smallest, we do this in two phases: find the champion, and then find the best of the remaining contenders by explicitly ignoring the champion's index.
  • An alternative approach is to sort the entire array in descending order and simply pick the element at index 1, but sorting takes O(n log n) time, making this two-pass O(n) approach mathematically faster.

Complexity

Time Complexity O(n)
Space Complexity O(n)
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