Dutch Flag Problem

Q.) Given an array containing lower case and upper case alphabets and numbers, how can you sort/arrange the array in one single pass using just one variable for swapping such that the resultant array should put the input elements into 3 buckets in the following fashion - Input - aA1B23Cbc4 Output - abcABC1234 Note - ordering doesn't matter the output could be - ABC1234abc or 1234abcABC You just have to arrange the data into 3 buckets in single pass using just one temp variable for swapping. Expected runtime - O(n) and O(1) extra space.

Solution:

#include"stdio.h"
int main()
{
    int Size,i;
    scanf("%d",&Size);
    char arr[Size+1];
    scanf("%s",arr);
    int low=0,mid=1,high=Size-1;
    while(mid<=high)
    {
        if(arr[mid]>='0' && arr[mid]<='9')
        {
            arr[mid]=arr[low]+arr[mid]-(arr[low]=arr[mid]);
            low++;
            mid++;
        }
        else if(arr[mid]>='a' && arr[mid]<='z')
            mid++;
        else if(arr[mid]>='A' && arr[mid]<='Z')
        {
            arr[mid]=arr[high]+arr[mid]-(arr[high]=arr[mid]);
            high--;
        }
    }
    printf("%s",arr);
    return 0;
}