Leetcode 97: Interleaving String

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 = "aabcc",
s2 = "dbbca",

When s3 = "aadbbcbcac", return true.
When s3 = "aadbbbaccc", return false.

 

 

 

public class Solution {
    public bool IsInterleave(string s1, string s2, string s3) {
        int len1 = s1.Length, len2 = s2.Length, len3 = s3.Length;
        
        if (len1 == 0 || len2 == 0)
        {
            return len1 == 0 ? s2 == s3 : s1 == s3;
        }
        
        if (len3 != len1 + len2) return false;
        
        var dp = new bool[len1 + 1, len2 + 1];
        
        for (int i = 0; i <= len1; i++)
        {
            for (int j = 0; j <= len2; j++)
            {
                if (i == 0 && j == 0)
                {
                    dp[i, j] = true;                        
                }
                else if (i == 0)
                {
                    dp[i, j] = s2.Substring(0, j) == s3.Substring(0, j);  
                }
                else if (j == 0)
                {
                    dp[i, j] = s1.Substring(0, i) == s3.Substring(0, i);  
                }
                else
                {
                    dp[i, j] = (s1[i - 1] == s3[i + j -1] && dp[i - 1, j]) || (s2[j - 1] == s3[i + j -1] && dp[i, j - 1]);
                } 
            }
        }
        
        return dp[len1, len2];
    }
}