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### Program to Print Duplicate Element of an Array - C, C++ Code

Write a C, C++ program to print duplicate element of an array. Given an array, Only one element in an array is repeated, print a duplicate element.

C, C++ Interview Questions

Method 1 - Naive Approach

Use two for loops, Compare each element of an array with other element. The time complexity of this approach is  O(n2).

## C Program to Print Duplicate Element in an Array

``` #include <stdio.h>

int main(void) {

int arr, i, j, size;

printf("Enter the size of an array \n");
scanf("%d",&size);

printf("Enter the elements in an array\n");

for( i = 0; i < size; i++) {
scanf("%d", &arr[i]);
}

/* Logic to print duplicate
element of an array */

for(i = 0; i < size; i++){
for(j=i+1; j < size; j++){

if(arr[i] == arr[j]){

printf("Duplicate element in an array is %d ",arr[i]);
break;
}
}
}

return 0;
}

```

Output -

Enter the size of an array   5

Enter the elements in an array  2   3   6   5   3

Duplicate element in an array is  3

Method 2 - Use hashing

In this approach, We are using C++ map library. The time complexity of this program is O(n).

### C ++ code to Find Duplicate Element in Array

```#include <iostream>
#include <map>

using namespace std;

int main() {

int arr, i, size;

cout <<"Enter the size of an array\n";
cin  >> size;

cout <<"Enter elements in an array \n";

for(i = 0; i < size; i++) {
cin >> arr[i];
}

// Map STL library implementation
map<int, int> hash;

/* Make key and value pair.
key denotes the element
value is the count of that element.
*/
for(i = 0; i < size; i++) {
hash[arr[i]] = hash[arr[i]] + 1;
}

/* Check the count and if
count is greater than 1 then
print the element */

for(i = 0; i < size; i++){

if (hash[arr[i]] > 1){
cout<<"Repeated element is "<< arr[i];
break;
}
}

return 0;
}

```

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