Isomorphic strings in LeetCode

I solved this problem:


Given two strings s and t, determine if they are isomorphic.


Two strings are isomorphic if the characters in s can be replaced to
get t.


All occurrences of a character must be replaced with another character
while preserving the order of characters. No two characters may map to
the same character but a character may map to itself.

For example:


Given "egg", "add", return true.


Given "foo", "bar", return false.


Given "paper", "title", return true.

Note:


You may assume both s and t have the same length.

The code in C# on average took around 109ms to execute, which is pretty slow compared to the C++ version of the same algorithm, which executes in under 6ms. Although, the fastest C# solution for this problem is around 100ms.

public class Solution {
    public bool IsIsomorphic(string s, string t) {
            int[] map = Enumerable.Repeat(-1, 175).ToArray();
            bool[] marked = Enumerable.Repeat(false, 175).ToArray();
            for(int i=0; i<s.Length; ++i)
            {
                if (map[s[i]] ==  -1) // Unvisited 
                {
                    if (marked[t[i]]) // Already has a mapping
                    {
                        return false;
                    }

                    marked[t[i]] = true;

                    map[s[i]] = t[i];
                }
                else if(map[s[i]] != t[i])
                {
                    return false;
                }
            }

            return true;
    }
}

Optimizations I had done:

• Converted List to array after reading this

• Changed foreach to a plain for loop that helped remove another index variable for iterating over string t

Can you suggest any better way to squeeze some performance from the C# implementation?

And from the FAQ section of LeetCode I could see that C# uses mono 4.2.1 and C++ uses g++ 5.4.0.

I'm attaching the C++ solution as well just for reference:

```
#define MAX

I don't know how much runtime you'll save, but you're iterating 175 more times than you need to here.

int[] map = Enumerable.Repeat(-1, 175).ToArray();
bool[] marked = Enumerable.Repeat(false, 175).ToArray();

You can replace this with an old fashioned for loop and set them both at once.

const int maxChars = 175;

int[] map = new int[maxChars];
bool[] marked = new bool[maxChars];

for (var i = 0; i < maxChars; i++)
{
    map[i] = -1; 
    marked[i] = false;
}

It's more verbose, but might save you a millisecond or 2.

StackExchange Code Review Q#148265, answer score: 4