Give an array or string and our problem is how to reverse this array(string)
Examples :
Input : arr[] = {9, 2, 3}
Output : arr[] = {3, 2, 9}
Input : arr[] = {8, 5, 10, 3}
Output : arr[] = {3, 10, 5, 8}
Method 1 :- Recursive way
- Define Start as 0 and end as n-1
- swap the arr[start] and arr[end]
- Recursively call the rest of the array.
Implementation of this method is given below
#include <stdio.h>
int main() {
void reverseArr(int arr[],int start, int end)
{
if(start<end)
{
int temp;
temp=arr[start];
arr[start]=arr[end];
arr[end]=temp;
reverseArr(arr, start+1, end-1);
}
else return;
}
void printArr(int arr[],int size)
{
for(int i=0;i<size;i++)
{
printf("%d ",arr[i]);
}
}
int arr[] = {8, 5, 10, 3};
printArr(arr, 4);
printf("\n");
reverseArr(arr, 0, 3);
printf("Reversed array is \n");
printArr(arr, 4);
return 0;
}
Output :
8 5 10 3 Reversed array is 3 10 5 8
Time Complexity : O(n)
Method 2: Iterative Method
- Define start and end indexes as 0 and n-1 respectively
- in a loop swap arr[start] and arr[end]. and increase start by 1 and decrease end by 1.
Below is the implementation of the program
int main() {
void reverseArr(int arr[], int start, int end)
{
while (start < end)
{
int temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
start++;
end--;
}
}
void printArr(int arr[],int size)
{
for(int i=0;i<size;i++)
{
printf("%d ",arr[i]);
}
}
int arr[] = {8, 5, 10, 3};
printArr(arr, 4);
printf("\n");
reverseArr(arr, 0, 3);
printf("Reversed array is \n");
printArr(arr, 4);
return 0;
}
Output :
8 5 10 3 Reversed array is 3 10 5 8
Time Complexity : O(n)
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