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How to get rid of Java TLE problem

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  • Difficulty Level : Medium
  • Last Updated : 23 Mar, 2022
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It happens many times that you have written correct Java code with as much optimization as needed according to the constraints. But, you get TLE ????. 
This happens due to the time taken by Java to take input and write output using Scanner class which is slow as compared to BufferedReader and StringBuffer class. Read in detail about Scanner Class here
Have a look at some tips to get rid of this TLE issue (when your logic is correct obviously)? 
 

Tip 1 : Avoid using Scanner Class and try to use BufferedReader class
Tip 2 : Try to use StringBuffer class in case you have to print large number of data.

Let’s take a problem from GeeksforGeeks practice and solve the TLE issue: 
Problem : Segregate an Array of 0s, 1s and 2s 
In short, problem is, given an array of 0s, 1s and 2s. We have to segregate all the 0s in starting of array, all the 1s in mid of the array, and all the 2s in last of the array. 
Examples: 
 

Input : 1 1 2 0 0 2 1
Output : 0 0 1 1 1 2 2

Approach : Segregate array of 0s, 1s and 2s
Below is the implementation of above Approach : 
 

Java




// Program to segregate the
// array of 0s, 1s and 2s
import java.util.*;
import java.lang.*;
import java.io.*;
class GFG {
    public static void main(String[] args)
    {
        // Using Scanner class to take input
        Scanner sc = new Scanner(System.in);
 
        // Number of testcase input
        int t = sc.nextInt();
 
        // Iterating through all the testcases
        while (t-- > 0) {
 
            // Input n, i.e. size of array
            int n = sc.nextInt();
 
            int arr[] = new int[n];
 
            // Taking input of array elements
            for (int i = 0; i < n; i++)
                arr[i] = sc.nextInt();
 
            // Calling function to segregate
            // input array
            segregateArr(arr, n);
 
            // printing the modified array
            for (int i = 0; i < n; i++) {
                System.out.print(arr[i] + " ");
            }
 
            System.out.println();
        }
        sc.close();
    }
 
    // Function to segregate 0s, 1s and 2s
    public static void segregateArr(int arr[], int n)
    {
        /*
        low : to keep left index
        high : to keep right index
        mid : to get middle element
        */
        int low = 0, high = n - 1, mid = 0;
 
        // Iterating through the array and
        // segregating elements
        while (mid <= high) {
 
            // If element at mid is 0
            // move it to left
            if (arr[mid] == 0) {
                int temp = arr[low];
                arr[low] = arr[mid];
                arr[mid] = temp;
                low++;
                mid++;
            }
 
            // If element at mid is 1
            // nothing to do
            else if (arr[mid] == 1) {
                mid++;
            }
 
            // If element at mid is 2
            // move it to last
            else {
                int temp = arr[mid];
                arr[mid] = arr[high];
                arr[high] = temp;
                high--;
            }
        }
    }
}

According to our expectations, it should pass all the testcases and get accepted on GeeksforGeeks practice. But, when we submit this code on GeeksforGeeks IDE, it shows TLE. 
 

This signifies that we have exceeded the time limit as expected. Not an issue, let’s use the tips given above
 

  1. Use BufferedReader to take input.
  2. Use StringBuffer to save and print output.

Approach : Segregate array of 0s, 1s and 2s
Below is the implementation of Java code for segregating 0s, 1s and 2s 
 

Java




// Java program to segregate
// array of 0s, 1s and 2s
import java.io.*;
import java.util.*;
 
class GFG {
    // Driver Code
    public static void main(String[] args) throws IOException
    {
 
        // Using BufferedReader class to take input
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
        // taking input of number of testcase
        int t = Integer.parseInt(br.readLine());
 
        while (t-- > 0) {
            // n : size of array
            int n = Integer.parseInt(br.readLine());
 
            // Declaring array
            int arr[] = new int[n];
 
            // to read multiple integers line
            String line = br.readLine();
            String[] strs = line.trim().split("\\s+");
 
            // array elements input
            for (int i = 0; i < n; i++)
                arr[i] = Integer.parseInt(strs[i]);
 
            // Calling Functions to segregate Array elements
            segregateArr(arr, n);
 
            // Using string buffer to append each output in a string
            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < n; i++)
                sb.append(arr[i] + " ");
 
            // finally printing the string
            System.out.println(sb);
        }
        br.close();
    }
 
    // Function to segregate 0s, 1s and 2s
    public static void segregateArr(int arr[], int n)
    {
        /*
        low : to keep left index
        high : to keep right index
        mid : to get middle element
        */
        int low = 0, high = n - 1, mid = 0;
 
        // Iterating through the array and
        // segregating elements
        while (mid <= high) {
 
            // If element at mid is 0
            // move it to left
            if (arr[mid] == 0) {
                int temp = arr[low];
                arr[low] = arr[mid];
                arr[mid] = temp;
                low++;
                mid++;
            }
 
            // If element at mid is 1
            // nothing to do
            else if (arr[mid] == 1) {
                mid++;
            }
 
            // If element at mid is 2
            // move it to last
            else {
                int temp = arr[mid];
                arr[mid] = arr[high];
                arr[high] = temp;
                high--;
            }
        }
    }
}

Great! You have leveled up. 
Java TLE issue? Seems pretty much simple :). You may try it now.
 


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