程序查找数字n1的最小排列，但应大于另一个给定的数字n2； 如果可能，打印“无效”

Question

The problem deals with two input integers. We need to find permutation of n1 such that it's smallest greater integer to n2.

I have tried coding but I am not getting the correct output. I can't figure out how to print only the smallest permutation larger than n2. My code is printing all permutations larger than n2.

My Code:

        import java.util.*;
        class kbc{
        public static void main (String args[])  throws Exception {    
        int n1=124;
        int n2=320;
        String s1 = "";
        s1+= n1;
        String s2 = "";
        s2+= n2;
        if(s2.length()>s1.length())
        System.out.println("Invalid");
        else{
            int[] ad = new int[s1.length()];
            for (int i=0; i<s1.length();i++){
                ad[i]= s1.charAt(i)-'0';
            }
            printSmallest(ad,n2,0);
        }
    }
    static void printSmallest(int[] a, int n2, int k) 
    {
        int snum;
        int saved= Integer.MAX_VALUE;
        String s="";
        if (k == a.length) 
        {
            for (int i = 0; i < a.length; i++) 
            {
                s=s+a[i];
            }
            snum = Integer.parseInt(s);
             if(snum>n2){
            if(snum<saved){
                 saved=snum;
             }
             System.out.println(saved);
             }

         }

        else{ 
        for (int i = k; i < a.length; i++){
                int temp = a[k];
                a[k] = a[i];
                a[i] = temp;

                printSmallest(a,n2, k + 1);

                temp = a[k];
                a[k] = a[i];
                a[i] = temp;
        }
        }  
    }
}

Expected Output:

412

Code Output:

421
412

Answer 1

The way you are picking the characters for permutation, it is causing the problem. If you pick the characters at ascending order of their ASCII value then it will not be a problem. After getting your desired number, you can tell the recursion that "OK, I have found my answer, Don't call again". You can check this code. I changed your code not that much.

class kbc {

    private static boolean taken[];
    private static boolean found = false;
    public static void main (String args[])  throws Exception {    
        int n1=124;
        int n2=320;
        String s1 = "";
        s1+= n1;
        String s2 = "";
        s2+= n2;
        if(s2.length()>s1.length())
            System.out.println("Invalid");
        else {
            taken = new boolean[s1.length()];
            char[] ad = new char[s1.length()];
            char[] tempArray = s1.toCharArray();
            Arrays.sort(tempArray);
            s1 = new String(tempArray);
            printSmallest(ad, s1, n2,0);
        }
    }
    static void printSmallest(char[] a, String s1, int n2, int k) 
    {
        if(found)
            return;
        int snum;
        int saved= Integer.MAX_VALUE;
        String s="";
        if (k == a.length) 
        {
            for (int i = 0; i < a.length; i++) 
            {
                s=s+a[i];
            }
            snum = Integer.parseInt(s);
            if(snum>n2){
                if(snum<saved){
                    saved=snum;
                    found = true;
                }
                System.out.println(saved);
            }

        }
        else{ 
            for (int i = 0; i < a.length; i++){
                if(!taken[i] && !found) {
                    taken[i] = true;
                    a[k] = s1.charAt(i);
                    printSmallest(a, s1, n2, k + 1);
                    taken[i] = false;
                }
            }
        }  
    }
}