Smooth Sentences

A simple problem from edabit.com

Introduction

I found this simple problem online. I throught it would be a great example of how to use Arrays and string methods. In particular I'm using C#.

The Problem

You can find the problem here. The program I'm writing is supposed to tell if a sentence passed as input is a Smooth Sentence.

What is a Smooth Sentence?

A smooth sentence is a sentence where the last letter of each word is identical to the first letter of the following word.

Explanation

Firstly, we have to find a way to get every single word from the input sentence.

We can do that with the Split() method, which returns an Array of strings. This method accepts a string argument, the separator.

In this case, we can separate each word from the sentence by using a blank space as the separator.

Let's write the first part of the method.

public static bool IsSmooth(string sentence)
{
    string[] sentences = sentence.Split(' ');
}

Next, we have to check if the last character of the initial word and the first character of the previous word are equal.

To do so, we need a loop going from 0 to the length of the array - 1. The -1 ensures we never get out of the Array's boundaries.

for (int i = 0; i < sentences.Length - 1; i++)
{
    ...
}

We'll also need to find the two characters we need to check against each other.

The Substring() method, lets us take part in a string, for instance, we're taking the last char of the initial word

previousWord.Substring(previousWord.Length - 1)

and the first char of the following word.

followingWord.Substring(0, 1)

Then, we can convert the substrings to characters using Char.parse().

string previousWord = sentences[i];
char lastChar = Char.Parse(previousWord.Substring(previousWord.Length - 1));

string followingWord = sentences[i + 1];
char firstChar = Char.Parse(followingWord.Substring(0, 1));

Finally, we can check if the two words follow the rules of the problem.

If we return false as soon as any word fails the test, we can make sure the program doesn't go through the loop pointlessly.

If the method doesn't return before the end of the loop, we can return true.

Tweaks and fixes

To avoid crashes, we should make sure that the sentence doesn't start nor end with white spaces. It's possible to do that using Trim().

Moreover, the check we're performing on the characters is case-sensitive so, we should convert the sentence to lower case with ToLower().

At the end, if the sentence contains less than one character, we should return false.

if (sentence.Length <= 1) return false;

Solution

public static bool IsSmooth(string sentence)
{
    sentence = sentence.Trim().ToLower();
    string[] sentences = sentence.Split(' ');

    if (sentence.Length <= 1) return false;

    for (int i = 0; i < sentences.Length - 1; i++)
    {
        string previousWord = sentences[i];
        char lastChar = Char.Parse(previousWord.Substring(previousWord.Length - 1));

        string followingWord = sentences[i + 1];
        char firstChar = Char.Parse(followingWord.Substring(0, 1));

        if (lastChar != firstChar) return false;
    }

    return true;
}

IsSmooth("Marta appreciated deep perpendicular right trapezoids") ➞ true

IsSmooth("Someone is outside the doorway") ➞ false

IsSmooth("She eats super righteously") ➞ true