Fast Input/Output methods for different languages

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Introduction

Efficient handling of Input/Output (I/O) operations is crucial in programming competitions, especially when dealing with large datasets. This document provides optimized techniques for I/O in Java, C++, and Python.

Java: Using BufferedReader for Faster I/O

Why BufferedReader?

  • Scanner vs. BufferedReader: Scanner is slower than BufferedReader due to its internal parsing mechanics and smaller buffer size.
  • Advantages of BufferedReader: It reads a larger block of characters into the buffer, reducing the number of I/O operations, thus making it more suitable for handling large inputs.

Example of Using BufferedReader

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class FastIO {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line;
        while ((line = br.readLine()) != null) {
            // Process the line
        }
        br.close();
    }
}

Additional Example with BufferedReader

Reading an integer T denoting the number of test cases, followed by T lines, each containing two integers a and b:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class TestCasesIO {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine());
        for (int i = 0; i < T; i++) {
            String[] input = br.readLine().split(” “);
            int a = Integer.parseInt(input[0]);
            int b = Integer.parseInt(input[1]);
            // Process a and b
        }
        br.close();
    }
}

C++: Optimizing I/O Operations

Using Scanf

  • scanf is typically faster than cin.
  • Example: scanf(“%d”, &variable);

Faster I/O with ios_base::sync_with_stdio(false)

Example

#include <iostream>
using namespace std;
int main() {
    ios_base::sync_with_stdio(false);
    int a;
    cin >> a;
    // Rest of the code
}

Advanced I/O Optimization in C++

Example with Advanced Optimizations

#include <iostream>
using namespace std;
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    // Your code here
}

Key Points

  • Disabling Synchronization: ios_base::sync_with_stdio(0); disables synchronization between the standard C and C++ I/O streams.
  • Untying cin from cout: cin.tie(0); and cout.tie(0); unties cin from cout.
  • Avoiding endl: Use “\n” instead of endl for newlines to avoid unnecessary flushing of the buffer.

Concerns

  • Buffer Flushing: Using endl frequently can degrade performance.
  • Mixed I/O: Mixing C-style and C+±style I/O can lead to undefined behavior when synchronization is turned off.

Python: Standard I/O Handling

General Guidance

  • Python’s input() and print() should suffice for most problems.
  • For large inputs, use sys.stdin.readline().

Example Using sys.stdin.readline()

import sys
for line in sys.stdin:
    # Process the line