TLE in JNEXT problem in SPOJ

Question

Problem Statement: JNEXT

DevG was challanged to find the just next greater number which can be formed using digits of a given number. Now DevG needs your help to find that just next greater number and win the challenge.

Input

The first line have t number of test cases (1 <= t <= 100). In next 2*t lines for each test case first there is number n (1 <= n <= 1000000) which denotes the number of digits in given number and next line contains n digits of given number separated by space.

Output

Print the just next greater number if possible else print -1 in one line for each test case.

Note : There will be no test case which contains zero in starting digits of any given number.

Example

Input:

2
5
1 5 4 8 3
10
1 4 7 4 5 8 4 1 2 6

Output:

15834
1474584162

My Solution is

public static void main(String[] argh) throws Exception{
        Reader br = new Reader();
        int t= br.nextInt();

        for(int aa=0; aa<t; aa++){
            int n= br.nextInt();
            int[] arr= new int[n];
            int breakPoint= -1;
            int mI= -1;

            for(int qq=0; qq<n; qq++){
                arr[qq]= br.nextInt();
                if(qq !=0 && arr[qq] > arr[qq-1]){
                    breakPoint= qq-1;
                }
                if(breakPoint != -1){
                    if(arr[breakPoint] < arr[qq]){
                        mI= qq;
                    }
                }
            }
            if(breakPoint == -1 || n == 1){
                System.out.println(-1);
                continue;
            }

            // swap
            arr[breakPoint]= arr[breakPoint] + arr[mI];
            arr[mI]= arr[breakPoint] - arr[mI];
            arr[breakPoint]= arr[breakPoint] - arr[mI];
            breakPoint++;

            for(int ii=0; ii<breakPoint; ii++){
                System.out.print(arr[ii]);
            }
            for(int ii=n-1; ii>=breakPoint; ii--){
                System.out.print(arr[ii]);
            }
            System.out.println("");
        }
    }

My solution is having O(N) time complexity but still I am getting TLE. Can anyone point out issue?

Answer 1

int[] arr

You can probably create it only once, with maximum possible size, outside for for loop.

System.out.print(arr[ii]);

You need to use StringBuilder and output only whole string in single println call. Multiple System.out.print calls are what makes it slow.

Answer 2

It indeed looks like your code is O(n), I atleast can't find a reason for it not to be. Although I would recommend some better variable names and breaking out done functions.

Your code uses Reader which to my knowledge is unbuffered and thus very slow. It is reasonably common for inappropriate IO code in Java programming challenges to cause TLE even for the correct algorithm. Considering you're reading up to one million ints per test case, this could be your suspect.

Try wrapping the Reader in a BufferedReader .

While I believe that the system out stream is buffered, you can also build the output into a StringBuilder to see if that makes a difference.

For reference: https://www.hackerearth.com/practice/notes/inputoutput-in-javascanner-bufferedreader-self-made-fast-io/