Merging elements of two different arrays alternatively in third array in C++.

Problem statement

Given two arrays, we need to combine two arrays in such a way that the combined array has alternate elements of the first and second array. If one of the arrays has an extra element, then these elements should be appended at the end of the combined array.

arr1[] = {10, 20, 30, 40}
arr2[] = {-10, -20, -30, -40}
result[] = {10, -10, 20, -20, 30, -30, 40, -40}

Algorithm

1. Traverse both arrays and one by one put elements into result array.
2. If one of the array exhausts then put remaining elements of other array into result array.

Example

#include <iostream>
#define SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
using namespace std;
void alternateMergedArray(int *arr1, int n1, int *arr2, int n2,int *result){
   int i, j, k;
   i = 0;
   j = 0;
   k = 0;
   while (i < n1 && j < n2) {
      result[k] = arr1[i];
      ++k;
      ++i;
      result[k] = arr2[j];
      ++k;
      ++j;
   }
   while (i < n1) {
      result[k] = arr1[i];
      ++k;
      ++i;
   }
   while (j < n2) {
      result[k] = arr2[j];
      ++k;
      ++j;
   }
}
void displayArray(int *arr, int n){
   for (int i = 0; i < n; ++i) {
      cout << arr[i] << " ";
   }
   cout << endl;
}
int main(){
   int arr1[] = {10, 20, 30, 40};
   int arr2[] = {-10, -20, -30, -40};
   int result[SIZE(arr1) + SIZE(arr2)];
   cout << "First array: " << endl;
   displayArray(arr1, SIZE(arr1));
   cout << "Second array: " << endl;
   displayArray(arr2, SIZE(arr2));
   cout << "Result array: " << endl;
   alternateMergedArray(arr1, SIZE(arr1), arr2, SIZE(arr2),result);
   displayArray(result, SIZE(result));
   return 0;
}

Output

When you compile and execute the above program. It generates the following output −

First array:
10 20 30 40
Second array:
-10 -20 -30 -40
Result array:
10 -10 20 -20 30 -30 40 -40