Evaluative

2 minutes to read

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

Evaluative 1

Problem

We need to write a program that is evaluate a polynomial with given coefficients at a given value . For example:

"1 -2 3 -4 5 -6 7 -8 9", "5" -> "2983941"

Solution

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

C

#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main() {
  // take in the numbers
  char input[4096] = { 0 };
  fgets(input, sizeof(input), stdin);
  long coeffs[1024] = { 0 };
  
  char* token = strtok(input, " ");
  int i = 0;

  while (token != NULL) {
    coeffs[i++] = atol(token);
    token = strtok(NULL, " ");
  }

  int length = i;

  long x = 0;
  scanf("%ld", &x);

  // calculate answer 
  long answer = 0;

  for (i = 0; i < length; i++) {
    answer += coeffs[i] * (long) pow(x, i);
  }

  // print answer
  printf("%ld\n", answer);

  return 0;
}

C++

#include <cmath>
#include <iostream>
#include <sstream>
#include <vector>

int main() {
  // take in the coeffs
  std::string s;
  std::vector<long> coeffs;
  long n;
  
  std::getline(std::cin, s);
  std::istringstream iss(s);

  while (iss >> n) {
    coeffs.push_back(n);
  }

  long x;
  std::cin >> x;

  // calculate answer 
  long answer = 0;

  for (long i = 0; i < coeffs.size(); i++) {
    answer += coeffs[i] * (long) pow(x, i);
  }

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

  return 0;
}

Python

# take in the number
coeffs = map(int, input().split())
x = int(input())

# calculate answer
answer = sum(c * x ** i for i, c in enumerate(coeffs))

# print answer
print(answer)

Rust

use std::io;

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

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

    let coeffs: Vec<i64> = input
        .trim()
        .split(" ")
        .map(|s| s.parse().expect("Please enter a valid number"))
        .collect();

    input.clear();

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

    let x: i64 = input.trim().parse().expect("Please enter a valid number");

    // calculate answer
    let answer: i64 = coeffs
        .iter()
        .enumerate()
        .map(|(i, c)| c * x.pow(i as u32))
        .sum();

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

Flag

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

HTB{eV4LuaT1nG_p0LyN0M1aL5_f0R_7H3_w1N}