Problem:
Score : 400 points

Problem Statement

A positive integer X is said to be a lunlun number if and only if the following condition is satisfied:

In the base ten representation of X (without leading zeros), for every pair of two adjacent digits, the absolute difference of those digits is at most 1.

For example, 1234, 1, and 334 are lunlun numbers, while none of 31415, 119, or 13579 is.

You are given a positive integer K. Find the K-th smallest lunlun number.

Constraints

1 \leq K \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

K

Output

Print the answer.

Sample Input 1

15

Sample Output 1

23

We will list the 15 smallest lunlun numbers in ascending order:

1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
21,
22,
23.

Thus, the answer is 23.

Sample Input 2

1

Sample Output 2

1

Sample Input 3

13

Sample Output 3

21

Sample Input 4

100000

Sample Output 4

3234566667

Note that the answer may not fit into the 32-bit signed integer type.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;
import static java.lang.System.out;

public class Main{
    static MyReader in = new MyReader();
    static int K;
    public static void main(String[] args){
        K = in.i();
        LinkedList<Long>[][] list = new LinkedList[11][10];
        for (int d = 0; d <= 10; d++) {
            list[d] = new LinkedList[10];
            for (int i = 0; i < 10; i++) {
                list[d][i] = new LinkedList<>();
            }
        }
        for (int i = 0; i < 10; i++) {
            list[1][i].add((long)i);
        }
        int count = 9;
        if (K < 10) {
            out.println(K);
            return;
        }
        for (int d = 2; d <= 10; d++) {
            for (int i = 0; i < 10; i++) {
                if (i - 1 >= 0) {
                    for (long x : list[d-1][i-1]) {
                        count = f(list, d, i, x, count);
                    }                     
                } 
                for (long x : list[d-1][i]) {
                    count = f(list, d, i, x, count);
                }    
                if (i + 1 <= 9) {
                    for (long x : list[d-1][i+1]) {
                        count = f(list, d, i, x, count);
                    }                     
                } 
            }
        }
    }

    static int f(LinkedList<Long>[][] list, int d, int i, long x, int count){
        long y = i * pow10(d - 1) + x;
        if(i != 0) {
            count++;
        }
        if (count == K) {
            out.println(y);
            System.exit(0);
        } else {
            list[d][i].add(y);              
        }
        return count;
    }
    
    static long pow10(int d){
        long ret = 1;
        for (int i = 0 ; i < d; i++) {
            ret *= 10;
        }
        return ret;
    }

    static class MyReader extends BufferedReader{
        MyReader(){
            super(new InputStreamReader(System.in));
        }

        String s(){
            try{return readLine();}catch(IOException e){return "";}
        }

        String[] ss(){
            return s().split(" ");
        }

        int i(){
            return Integer.parseInt(s());
        }

        int[] ii(){
            String[] ss = ss();
            int[] ii = new int[ss.length];
            for(int j = 0; j < ss.length; j++) ii[j] = Integer.parseInt(ss[j]);
            return ii;
        }

        ArrayList<Integer> li(){
            String[] ss = ss();
            ArrayList<Integer> li = new ArrayList<>();
            for(int j = 0; j < ss.length; j++) li.add(Integer.parseInt(ss[j]));
            return li;
        }

        long l(){
            return Long.parseLong(s());
        }

        long[] ll(){
            String[] ss = ss();
            long[] ll = new long[ss.length];
            for(int j = 0; j < ss.length; j++) ll[j] = Long.parseLong(ss[j]);
            return ll;
        }
    }
}