Replacement

2 minutes to read

We are given the following website to write a coding solution:

Replacement 1

Problem

We need to write a program that is able to take a text string and two additional characters to replace one for the other. For instance:

"asdf" "s" "b" -> "abdf"

Solution

Since we are allowed to use C, C++, Python and Rust, let’s write a solution on every language, just because.

C

#include <stdio.h>

int main() {
  // take in the strings
  char s[1024] = { 0 };
  char a;
  char b;
  fgets(s, sizeof(s), stdin);
  scanf("%c\n", &a);
  scanf("%c\n", &b);

  // calculate answer
  int i = -1;
  char answer[1024] = { 0 };

  while (s[++i]) {
    answer[i] = s[i] == a ? b : s[i];
  }

  // print answer
  printf("%s", answer);

  return 0;
}

C++

#include <algorithm>
#include <iostream>

int main() {
  // take in the string
  std::string s;
  getline(std::cin, s);
  char a = getchar();
  getchar();
  char b = getchar();
  getchar();

  // calculate answer
  std::string answer = s;
  replace(answer.begin(), answer.end(), a, b);

  // print answer
  std::cout << answer << std::endl;

  return 0;
}

Python

# take in the strings
s = input()
a = input()
b = input()

# calculate answer
answer = s.replace(a, b)

# print answer
print(answer)

Rust

use std::io;

fn main() {
    // take in the strings
    let mut s = String::new();

    io::stdin().read_line(&mut s).expect("Failed to read line");

    let mut input = String::new();

    io::stdin()
        .read_line(&mut input)
        .expect("Failed to read line");

    let a = input
        .chars()
        .nth(0)
        .expect("Please enter a valid character");

    input.clear();

    io::stdin()
        .read_line(&mut input)
        .expect("Failed to read line");

    let b = input
        .chars()
        .nth(0)
        .expect("Please enter a valid character");

    // calculate answer
    let answer = str::replace(&s.trim(), &a.to_string(), &b.to_string());

    // print answer
    println!("{}", answer);
}

Flag

Using any of these programs, we are able to solve the chalenge and capture the flag:

HTB{r3pLacE_th3_sTR1nG_t0_g3t_th3_bl1ng!!}