算法回文 C#

Question

Can anyone please help, what am I missing on my code? The part one is Calculate The Palindrome Level, my answers all correct, I just could not figure it out for the part two ie Sum of The Palindrome Level, I could not meet the answer

Palindrome Palindrome is a word, phrase, or sequence that reads the same backward as forward eg "madam", "nurses run", "23499432". When palindrome sequence is splited in half, the first sequence may be a palindrome too.

Part #1

"Palindrome Level" is how many times a palindrome sequence can be splited in half until the first sequence from splited is not a palindrome or until the first sequence is just a character. Palindrome level ignores space and case insensitive (if the sequence length is odd number, then after split the sequence, take the middle character to the first sequence: "madam" -> "mad")

For example:

-nurses run: nursesrun -> nurse (1 level)

-451545154: 451545154 -> 45154 -> 451 (2 level)

-dam madam mad: dammadammad -> dammad -> dam (2 level)

Part #2

Defined string's prefixes as all prefixes of a string nun in inun : n, nu, nun, nunin, nunini, nuninin, nunininu, nunininun

"Sum of the palindrome level" of all string's prefixes is calculated by add all palindrome level of all prefixes of a string.

For example :

abacaba : a(0), ab(0), aba(1), abac(0), abaca(0), abacab(0), abacaba(1) =>sum of the palindrome level :2

Below is my code

public class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine("Calculate Palindrome level");
        foreach (var test in _CreatePalindromeLevelTestWords())
        {
            _CheckAnswer(test.Key, test.Value, CalculatePalindromeLevel(test.Key));
        }
        Console.WriteLine("Sum of the palindrome level");
        //Your code goes here
        foreach (var test in _CreateSumOfPalindromeLevelTestWords())
        {
            _CheckAnswer(test.Key, test.Value, SumOfPalindromeLevel(test.Key));
        }

        Console.ReadKey();

    }


public static int CalculatePalindromeLevel(string word)
{
    string strRemovedSpaces = StringRemoveSpace(word).ToLower();
    string nextstr = strRemovedSpaces;
    int count = 0;

    bool palResult = isPal(nextstr);

    while(palResult)
    {
        count++;
        int strLength;
        if (nextstr.Length % 2 == 0)
        {
            strLength = Convert.ToInt32(Math.Floor((decimal)nextstr.Length / 2));
        }
        else
        {
            strLength = Convert.ToInt32(Math.Ceiling((decimal) nextstr.Length / 2));
        }
        nextstr = nextstr.Substring(0, strLength);
        palResult = isPal(nextstr);
    }

    return count;

}

public static int SumOfPalindromeLevel(string word)
{
    string strRemovedSpace = StringRemoveSpace(word).ToLower();
    string nextstr = "";
    int count = 0;

    for (int i = 1; i < strRemovedSpace.Length; i++)
    {
        nextstr = strRemovedSpace.Substring(0, i);
        var palResult = isPal(nextstr);
        if (palResult == true)
        {
            count++;
        }
    }
    return count;
}

public static string StringRemoveSpace(string w)
{
    string str = string.Join("", w.Split(default(string[]), StringSplitOptions.RemoveEmptyEntries));
    return str;
}

public static bool isPal(string s)
{
    int length = s.Length;
    for (int i = 0; i < length / 2; i++)
    {
        if (s[i] != s[length - i - 1])
            return false;
    }
    return true;
}


public static Dictionary<string,int> _CreatePalindromeLevelTestWords()
{
    return new Dictionary<string, int>
    {
        {"nurses run",1 },
        {"dam madam mad",2 },
        {"Sitis sit is s it is sitis",3 }
    };
}


public static Dictionary<string, int> _CreateSumOfPalindromeLevelTestWords()
{
    return new Dictionary<string, int>
    {
         {"nurses run",1 },
        {"dam madam mad",3},
        {"Sitis sit is s it is sitis",7}
    };
}

public static void _CheckAnswer(string question, int expected, int answer)
{
    Console.WriteLine(answer.Equals(expected) ? $"{question}:{answer} (Right)" : $"{question}:{answer}(Wrong: expected {expected})");
}
}

I'm struggling with the Part #2, it didn't match with the expected result. Could you please help, what am I missing with? My result for the dammadammad->2 and sitissitissitissitis->4, while it should meet 3 and 7 respectively. I don't think there's a relation among the part #1 and the part #2, but I include the part one, in case it does. I can not sleep :( and want to know the answer, I'm still trying to find it.

Answer 1

There are two issues.

1. You are counting a single character as a palindrome, that is not allowed.
2. You failed to take the last character in the string into account.

To prove this, modify your method to print out some debug information to the console, to match the example that is given: https://dotnetfiddle.net/dfOh30

int SumOfPalindromeLevel(string word)
{
    string strRemovedSpace = StringRemoveSpace(word).ToLower();
    string nextstr = "";
    int count =0;

    Console.Write("{0} => ", word);
    for(int i=1;i<strRemovedSpace.Length;i++)
    {
        nextstr = strRemovedSpace.Substring(0,i);
        var palResult = isPal(nextstr);
        
        Console.Write("{0}({1}) ", nextstr, palResult ? 1 : 0);
        if(palResult==true){
            count++;
        }
    }
    
    Console.WriteLine();
    Console.WriteLine("=> sum of palindrome level: {0}", count);
    return count;   
}

When you run this: SumOfPalindromeLevel("abacaba"); you will get the following output:

abacaba => a(1) ab(0) aba(1) abac(0) abaca(0) abacab(0) 
=> sum of palindrome level: 2

Even though the resulting value of 2 was expected, notice how the 'a' on its own is counted and the final character is not evaluated. We call this boundary conditions , you've managed to fail both boundaries ;)

This is the first place to check when you sometimes get the right answer but not always, this is a very common pitfall with these types of questions.

This was the expected output:

abacaba => a(0) ab(0) aba(1) abac(0) abaca(0) abacaba(1) 
=> sum of palindrome level: 2

So there are two changes to make:

bool isPal(string s)
{
    int length = s.Length;
    if (length > 1)
    {
        for (int i = 0; i < length / 2; i++)
        {
            if (s[i] != s[length - i - 1])
                return false;
        }
        return true;
    }
    return false;
}

Then in your SumOfPalindromeLevel method you need to iterate all the characters:
Change this:

for(int i=1; i<strRemovedSpace.Length; i++)

to:

for(int i=1; i<=strRemovedSpace.Length; i++)

But this is still only half of the equation. This still doesn't satisfy the requirement for dam madam mad .

If we take the hint:

when palindrome sequence is splitted in half, this first sequence may be a palindrome too

And we include the sum of the halfs of the strings in the result then we can get the score of 3 for dammadammad :

int SumOfPalindromeLevel(string word)
{
    string strRemovedSpace = StringRemoveSpace(word).ToLower();
    string nextstr = "";
    int count =0;

    Console.Write("{0} => ", word);
    for(int i=1;i<=strRemovedSpace.Length;i++)
    {
        nextstr = strRemovedSpace.Substring(0,i);
        var palResult = isPal(nextstr);
        
        Console.Write("{0}({1}) ", nextstr, palResult ? 1 : 0);
        if(palResult==true){
            count++;
        }
    }
    Console.WriteLine();

    while (strRemovedSpace.Length > 1)
    {
        strRemovedSpace = strRemovedSpace.Substring(0,(int)Math.Ceiling((double)strRemovedSpace.Length/2d));
        var palResult = isPal(strRemovedSpace);
        Console.Write("{0}({1}) ", strRemovedSpace, palResult ? 1 : 0);
        if(palResult==true){
            count++;
        }
        Console.WriteLine();
    }

    Console.WriteLine(word + " => sum of palindrome level: {0}", count);
    Console.WriteLine();
    return count;   
}

Which returns score of 3 for dam madam mad :

dammadammad => d(0) da(0) dam(0) damm(0) damma(0) dammad(1) dammada(0) dammadam(0) dammadamm(0) dammadamma(0) dammadammad(1) 
dammad(1) 
dam(0) 
da(0) 
d(0) 
dammadammad => sum of palindrome level: 3

But it still does not return 7 for Sitis sit is s it is sitis :

Sitis sit is s it is sitis => s(0) si(0) sit(0) siti(0) sitis(1) sitiss(0) sitissi(0) sitissit(0) sitissiti(0) sitissitis(1) sitissitiss(0) sitissitissi(0) sitissitissit(0) sitissitissiti(0) sitissitissitis(1) sitissitissitiss(0) sitissitissitissi(0) sitissitissitissit(0) sitissitissitissiti(0) sitissitissitissitis(1) 
sitissitis(1) 
sitis(1) 
sit(0) 
si(0) 
s(0) 
Sitis sit is s it is sitis => sum of palindrome level: 6

So that's me out, I'd love to study the original requirement in full, rather than through images, perhaps you can paste the actual text in?