Next greatest number

14.cpp

// For eg: 396 --> i=0 => and j = 2 swap(3,6) ==> 693 ==> sort(1..n) => 6 [93] => 639 (this is the required number)
int ngd(n){
  if number is sorted in ascedning order just swap last two digits
  if number is sorted in descending order impossible
  else {
    find the condition a[j] > a[j-1] from last and stop there
    let n1 = a[j]
    find next smallest greater digit than n1
    let n2 = a[i]
    swap(a[j], a[i])
    then sort(a[j+1..n])
    this is the next greatest number
  }
}