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## to Largest Series Product in the C Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

For example, for the input `'1027839564'`, the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

For the input `'73167176531330624919225119674426574742355349194934'`, the largest product for a series of 6 digits is 23520.

## Getting Started

Make sure you have read the C page on the Exercism site. This covers the basic information on setting up the development environment expected by the exercises.

## Passing the Tests

Get the first test compiling, linking and passing by following the three rules of test-driven development.

The included makefile can be used to create and run the tests using the `test` task.

``````make test
``````

Create just the functions you need to satisfy any compiler errors and get the test to fail. Then write just enough code to get the test to pass. Once you've done that, move onto the next test.

As you progress through the tests, take the time to refactor your implementation for readability and expressiveness and then go on to the next test.

Try to use standard C99 facilities in preference to writing your own low-level algorithms or facilities by hand.

## Source

A variation on Problem 8 at Project Euler http://projecteuler.net/problem=8

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### test_largest_series_product.c

``````#include "vendor/unity.h"
#include "../src/largest_series_product.h"

void setUp(void)
{
}

void tearDown(void)
{
}

void test_can_find_the_largest_product_of_2_with_numbers_in_order(void)
{
TEST_ASSERT_EQUAL(72, largest_series_product("0123456789", 2));
}

void test_can_find_the_largest_product_of_2(void)
{
TEST_IGNORE();               // delete this line to run test
TEST_ASSERT_EQUAL(48, largest_series_product("576802143", 2));
}

void test_finds_the_largest_product_if_span_equals_length(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(18, largest_series_product("29", 2));
}

void test_can_find_the_largest_product_of_3_with_numbers_in_order(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(504, largest_series_product("0123456789", 3));
}

void test_can_find_the_largest_product_of_3(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(270, largest_series_product("1027839564", 3));
}

void test_can_find_the_largest_product_of_5_with_numbers_in_order(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(15120, largest_series_product("0123456789", 5));
}

void test_can_get_the_largest_product_of_a_big_number(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(23520,
largest_series_product
("73167176531330624919225119674426574742355349194934", 6));
}

void test_can_get_the_largest_product_of_a_big_number_ii(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(28350,
largest_series_product
("52677741234314237566414902593461595376319419139427", 6));
}

void test_can_get_the_largest_product_of_a_big_number_project_euler(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL_INT64(23514624000,
largest_series_product
("7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450",
13));
}

void test_reports_zero_if_the_only_digits_are_zero(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(0, largest_series_product("0000", 2));
}

void test_reports_zero_if_all_spans_include_zero(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(0, largest_series_product("99099", 3));
}

void test_rejects_span_longer_than_string_length(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(-1, largest_series_product("123", 4));
}

void test_reports_1_for_empty_string_and_empty_product_(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(1, largest_series_product("", 0));
}

void test_reports_1_for_nonempty_string_and_empty_product_(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(1, largest_series_product("123", 0));
}

void test_rejects_empty_string_and_nonzero_span(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(-1, largest_series_product("", 1));
}

void test_rejects_invalid_character_in_digits(void)
{
TEST_IGNORE();
TEST_ASSERT_EQUAL(-1, largest_series_product("123a5", 2));
}

int main(void)
{
UnityBegin("largest_series_product.c");

RUN_TEST(test_can_find_the_largest_product_of_2_with_numbers_in_order);
RUN_TEST(test_can_find_the_largest_product_of_2);
RUN_TEST(test_finds_the_largest_product_if_span_equals_length);
RUN_TEST(test_can_find_the_largest_product_of_3_with_numbers_in_order);
RUN_TEST(test_can_find_the_largest_product_of_3);
RUN_TEST(test_can_find_the_largest_product_of_5_with_numbers_in_order);
RUN_TEST(test_can_get_the_largest_product_of_a_big_number);
RUN_TEST(test_can_get_the_largest_product_of_a_big_number_ii);
RUN_TEST(test_can_get_the_largest_product_of_a_big_number_project_euler);
RUN_TEST(test_reports_zero_if_the_only_digits_are_zero);
RUN_TEST(test_reports_zero_if_all_spans_include_zero);
RUN_TEST(test_rejects_span_longer_than_string_length);
RUN_TEST(test_reports_1_for_empty_string_and_empty_product_);
RUN_TEST(test_reports_1_for_nonempty_string_and_empty_product_);
RUN_TEST(test_rejects_empty_string_and_nonzero_span);
RUN_TEST(test_rejects_invalid_character_in_digits);

UnityEnd();
return 0;
}``````

### src/largest_series_product.c

``````#include "largest_series_product.h"
#include <ctype.h>
#include <stddef.h>

int64_t largest_series_product(const char *input, const int series)
{
if (series == 0)
return 1;
if ((input == NULL) || (series < 0) || (!isdigit(*input)))
return -1;

int i, len = 0;
int64_t tmp, res = 0;
while (*input) {
for (i = 1, tmp = *input - '0'; (i < series) && *(input + i);
i++) {
if (!isdigit(*(input + i)))
return -1;
tmp *= *(input + i) - '0';
}
if ((i == series) && (tmp > res))
res = tmp;
input++;
len++;
}
if (len < series)
return -1;

return res;
}``````

### src/largest_series_product.h

``````#ifndef LARGEST_SERIES_H
#define LARGEST_SERIES_H
#include <stdint.h>

int64_t largest_series_product(const char *input, const int series);

#endif``````