unfinished code - 1657 - two string close

Leetcode1657-TwoStringClose.cs

public class Solution {
    public bool CloseStrings(string word1, string word2) {
        if(word1.Length != word2.Length)
            return false; 
        
        var map = new int[26];
        for(int i = 0; i < 26; i++)
        {
            map[i] = -1;    
        }
        
        var result = runDFS(word1.ToCharArray(), word2.ToCharArray(), 0, map);
    }
    
    private bool runDFS(char[] a1, char[] a2, int start, int[] map)
    {
        var length = a1.Length; 
        if(start == length)
            return true; 
        
        var a1c = a1[index];
        var a2c = a2[index];
        var isSame = a1c == a2c;
        
        if(isSame || (map[a1c-'a'] != -1 && map[a1c-'a'] == (a2c-'a'))
        {
            return runDFS(a1, a2, start + 1);
        }
        else
        {
            //  convert a1c to a2c
            map[a1c-'a'] = a2c - 'a';
            map[a2c-'a'] = a1c - 'a';
            
            var result = runDFS(a1, a2, start + 1, map);
            if(result)
                return true;
            
            map[a1c-'a'] = -1; 
            map[a2c-'a'] = -1;
            
            // swap with any letter
        }
    }
    
}