[LeetCode] 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.

[Solution].java

public class Solution {
    public boolean isInterleave(String s1, String s2, String s3) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s1.length() + s2.length() != s3.length()) return false;
        int[][] dp = new int[s1.length() + 1][s2.length() + 1];
        return isInterleave(s1, 0, s2, 0, s3, 0, dp);
    }

    private boolean isInterleave(String s1, int s1pos,
            String s2, int s2pos, String s3, int s3pos, int[][] dp){
        if(s3pos == s3.length()) return true;
        if(dp[s1pos][s2pos] == 1) return false;
        boolean r = false;
        if(s1pos < s1.length() && s1.charAt(s1pos) == s3.charAt(s3pos)){
            boolean next = isInterleave(s1, s1pos + 1, s2, s2pos, s3, s3pos + 1, dp);
            if(!next) dp[s1pos + 1][s2pos] = 1;
            r |= next;
        }
        if(!r && s2pos < s2.length() && s2.charAt(s2pos) == s3.charAt(s3pos)){
            boolean next = isInterleave(s1, s1pos, s2, s2pos + 1, s3, s3pos + 1, dp);
            if(!next) dp[s1pos][s2pos + 1] = 1;
            r |= next;
        }
        return r;
    }
}