Find Next Decimal With Same Digits and Same number of Digits (i.e. input 112 output will be 151)

Sudarshan Kasar

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2 min read

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Dec 29, 2020

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/***
 * Following Integer
 *
 * You are writing out a list of numbers. Your list contains all numbers with exactly i digits in its decimal representation which are equal to i,
 * for each i between 1 and 9, inclusive. You are writing them out in ascending order. For example, you might be writing every number with two '1's and one '5'.
 * Your list would begin 115, 151, 511, 1015, 1051. Given N, the last number you wrote, compute what the next number in the list will be.
 * The number of 1s, 2s, ..., 9s is fixed but the number of 0s is arbitrary.
 *
 * Input:
 * Your program should read lines of text from standard input. Each line will contain a single integer n < 10^6.
 * Output:
 * For each input ingter n, print to standard output the next integer in the list, one integer per line.
 * */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;


public class Main {

  public static void main(String[] args) throws IOException {
    InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8);
    BufferedReader in = new BufferedReader(reader);
    String line;

    while ((line = in.readLine()) != null) {
      int inputNumber = Integer.parseInt(line);

      HashMap<Integer, Integer> digitWithOccurance =countDigitAndOccurance(inputNumber);
      digitWithOccurance.remove(0);//remove orbitrary digit

      int nextDecimal = nextDecimalRepresentationSameDigits(inputNumber, digitWithOccurance);

      System.out.println(nextDecimal);
    }
  }

  private static int nextDecimalRepresentationSameDigits(
      int inputNumber, HashMap<Integer, Integer> digitWithOccurance){
    int returnNumber = inputNumber;
    int decimalRepresentation = inputNumber + 1;
    boolean condition = true;

    while(condition){
      HashMap<Integer, Integer> newNumberDigitWithOccurance = countDigitAndOccurance(decimalRepresentation);
      newNumberDigitWithOccurance.remove(0);

      if(digitWithOccurance.equals(newNumberDigitWithOccurance)){
        returnNumber = decimalRepresentation;
        condition = false;
      } else {
        ++decimalRepresentation;
      }
    }

    return returnNumber;
  }

  private static HashMap<Integer, Integer> countDigitAndOccurance(int inputNumber) {
    String temp = "" + inputNumber;

    HashMap<Integer, Integer> digitOccurance = new HashMap();

    for (int i = 0; i < temp.length(); i++)
    {
      int key = Integer.parseInt(String.valueOf(temp.charAt(i)));

      if(digitOccurance.keySet().contains(key)) {
        int digitCount = digitOccurance.get(key) + 1;

        digitOccurance.put(key, digitCount);
      } else {
        digitOccurance.put(key, 1);
      }
    }

    return digitOccurance;
  }
}