NextGreaterElementIII.cpp

// C++ program to find the smallest number which greater than a given number
// and has same set of digits as given number
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
 
// Utility function to swap two digits
void swap(char *a, char *b)
{
    char temp = *a;
    *a = *b;
    *b = temp;
}
 
// Given a number as a char array number[], this function finds the
// next greater number.  It modifies the same array to store the result
void findNext(char number[], int n)
{
    int i, j;
 
    // I) Start from the right most digit and find the first digit that is
    // smaller than the digit next to it.
    for (i = n-1; i > 0; i--)
        if (number[i] > number[i-1])
           break;
 
    // If no such digit is found, then all digits are in descending order
    // means there cannot be a greater number with same set of digits
    if (i==0)
    {
        cout << "Next number is not possible";
        return;
    }
 
    // II) Find the smallest digit on right side of (i-1)'th digit that is
    // greater than number[i-1]
    int x = number[i-1], smallest = i;
    for (j = i+1; j < n; j++)
        if (number[j] > x && number[j] < number[smallest])
            smallest = j;
 
    // III) Swap the above found smallest digit with number[i-1]
    swap(&number[smallest], &number[i-1]);
 
    // IV) Sort the digits after (i-1) in ascending order
    sort(number + i, number + n);
 
    cout << "Next number with same set of digits is " << number;
 
    return;
}
 
// Driver program to test above function
int main()
{
    char digits[] = "534976";
    int n = strlen(digits);
    findNext(digits, n);
    return 0;
}