Leetcode 291: Word Pattern II

Given a pattern and a string str, find if str follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty substring in str.

Examples:

1. pattern = "abab", str = "redblueredblue" should return true.
2. pattern = "aaaa", str = "asdasdasdasd" should return true.
3. pattern = "aabb", str = "xyzabcxzyabc" should return false.

 

Notes:
You may assume both pattern and str contains only lowercase letters.

 

public class Solution {
    public bool WordPatternMatch(string pattern, string str) {
        return IsMatch(pattern, str, 0, 0, new Dictionary<char, string>(), new HashSet<string>());
    }
    
    private bool IsMatch(string pattern, string str, int pStart, int sStart, Dictionary<char, string> map, HashSet<string> hashset)
    {
        if (pStart >= pattern.Length || sStart >= str.Length)
        {
            return pStart >= pattern.Length && sStart >= str.Length;
        }
        
        if (map.ContainsKey(pattern[pStart]))
        {
            var s = map[pattern[pStart]];
            if (!str.Substring(sStart, str.Length - sStart).StartsWith(s))
            {
                return false;
            }
            
            return IsMatch(pattern, str, pStart + 1, sStart + s.Length, map, hashset);
        }
        else
        {
            for (int i = sStart; i < str.Length; i++)
            {
                var s = str.Substring(sStart, i - sStart + 1);
                
                if (!hashset.Contains(s))
                {
                    hashset.Add(s);
                    map[pattern[pStart]] = s;
                    
                    if (IsMatch(pattern, str, pStart + 1, i + 1, map, hashset))
                    {
                        return true;
                    }
                    
                    hashset.Remove(s);
                    map.Remove(pattern[pStart]);
                }
            }
        }
        
        return false;
    }
}