Day 9: factorial 3|| hackerrank || 30 days of code || programming_info

Objective
Today, we're learning and practicing an algorithmic concept called Recursion. Check out the Tutorial tab for learning materials and an instructional video!

Recursive Method for Calculating Factorial

Task
Write a factorial function that takes a positive integer,  as a parameter and prints the result of  ( factorial).

Note: If you fail to use recursion or fail to name your recursive function factorial or Factorial, you will get a score of .

Input Format

A single integer,  (the argument to pass to factorial).

Constraints

• Your submission must contain a recursive function named factorial.

Output Format

Print a single integer denoting .

Sample Input

3

Sample Output

6

Explanation

Consider the following steps:

From steps  and , we can say ; then when we apply the value from  to step , we get . Thus, we print  as our answer.

Solution using C language:

#include <assert.h>

#include <limits.h>

#include <math.h>

#include <stdbool.h>

#include <stddef.h>

#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

char* readline();

// Complete the factorial function below.

int factorial(int n) {

    if (n>=1)

        return n*factorial(n-1);

    else

        return 1;

}

int main()

{

    FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");

    char* n_endptr;

    char* n_str = readline();

    int n = strtol(n_str, &n_endptr, 10);

    if (n_endptr == n_str || *n_endptr != '\0') { exit(EXIT_FAILURE); }

    int result = factorial(n);

    fprintf(fptr, "%d\n", result);

    fclose(fptr);

    return 0;

}

char* readline() {

    size_t alloc_length = 1024;

    size_t data_length = 0;

    char* data = malloc(alloc_length);

    while (true) {

        char* cursor = data + data_length;

        char* line = fgets(cursor, alloc_length - data_length, stdin);

        if (!line) { break; }

        data_length += strlen(cursor);

        if (data_length < alloc_length - 1 || data[data_length - 1] == '\n') { break; }

        size_t new_length = alloc_length << 1;

        data = realloc(data, new_length);

        if (!data) { break; }

        alloc_length = new_length;

    }

    if (data[data_length - 1] == '\n') {

        data[data_length - 1] = '\0';

    }

    data = realloc(data, data_length);

    return data;

}

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