CareerCup

let us from an array which consists of digits of the given number as its element
for ex: number = 1234 then our array would be, arr[] = {1, 2, 3, 4}; and N = 4(length of array)

Then we do following steps to get the nextPermutation

1) find the highest index i such that arr[i] < arr[i+1];
2) next we find highest index j > i (found in step 1) , such that arr[j] > arr[i] , such j is sure to exist because we already have it as i+1 , we want the highest index
3)swap arr[i], arr[j].
4)reverse the array arr from index i+1 to N

and we get our next permutation

following code implements , the above algorithm
It takes as input the array arr and its length

bool nextPermutation(int arr[], int N)
{
     int i, pos, maxPos, t;
     
//step1)
     pos = maxPos = -1;
     for (i=0; i < N-1; i++)
         if (arr[i] < arr[i+1])
            pos = i;
           
    // if there is no such i such that arr[i] < arr[i+1] then the given number has no next  permutatio                                                 if (pos == -1) 
        return false;

//step2)     
     for (i=pos+1; i < N; i++)
         if (arr[pos] < arr[i])
            maxPos = i;
     
//step3) swap
     t = arr[pos];
     arr[pos] = arr[maxPos];
     arr[maxPos] = t;
     
//step4)
     // reverse arr[pos+1..N]
     for (i=pos+1; i < (N+pos+1)/2; i++)
     {
         t = arr[i];
         arr[i] = arr[N-i+pos];
         arr[N-i+pos] = t;
     }

     //for (i=0; i < N; i++)
          //printf("%d ", arr[i]);
     return true;
}

Does the question ask for the least number which is greater than the given number and is also the permutation of it?

I think it requires flipping the first instance of arr[i] < arr[i+1], starting from units position. The idea is to make the least significant two digits more than it's current value. (Comments?)

retNextPermute(char* num) //assuming the num to be string.
{
int len = strlen(num);
for(; len > 1; len--)
{
//compare the two digits
int x = num[len-1] - '0';
int y = num[len-2] - '0';
if(x > y)
{
//flip the digits if condition satisfy and break
char tmp = num[len-1];
num[len-1] = num[len-2];
num[len-2] = tmp;
break;
}
}
//print the num
}

Anonymous !
it requires to find the highest index i such that a[i]<a[i+1].
then make it
temp = a[i];
a[i]=a[i+1];
swap shift the elements from a[i+2] to N to left by one position and put a[i+1] at the end .

sorry its following
temp = a[i];
a[i]=a[i+1];
sort the elements a[i+1] to N in ascending order and put the elements in the position a[i+1] to N.