Given a number, find the next larger number using the same digits.

Solution #1:

Algorithm:
- Move from right -> left and stop when the current digit is greater than the next one, let's call this point, 'hotspot'.
- Sort all the digits from hotspot till the end of the number in increasing order.
- Swap the digit on the left of the 'hotspot' with the last digit of the new number.

e.g.
5784321
hotspot: 8
after sorting: 5712348
after swapping: 5812347

Here is the code,

void nextLarge(char* num)
{
    int len = strlen(num);
    int i;

    //decrement i till digits are increasing from right to left
    for(i=len-1; num[i] < num[i-1]; i--)
    {
        //return if the digits are sorted in decreasing
        //order, number is already the largest.
        if(i == 1)
            return;
    }

    //sort everything from hotspot till the end
    sort(num, i, len-1);

    //swap digit before hotspot with the last one
    swap(&(num[i-1]), &(num[len-1]));
}

int main()
{
    char num[20] = {0, };

    sprintf(num, "%s", "5417962");
    
    nextLarge(num);

    printf("%s\n", num);

    return 0;
}