1 public class Solution {
 2     public boolean isInterleave(String s1, String s2, String s3) {
 3         int len1 = s1.length();
 4         int len2 = s2.length();
 5         int len3 = s3.length();
 6         if(len1+len2!=len3) return false;
 7         boolean[][] match= new boolean[len1+1][len2+1];//define [][] is the length of the string! [0] means "null"
 8         int i =1;//should from 1
 9         match[0][0]=true;
10         while(i<=len1 &&s1.charAt(i-1)==s3.charAt(i-1)){
11             match[i][0]=true;
12             i++;
13         }
14         i=1;
15         while(i<=len2 &&s2.charAt(i-1)==s3.charAt(i-1)){
16             match[0][i]=true;
17             i++;
18         }
19         for(int m=1;m<=len1;m++){
20             for(int n=1;n<=len2;n++){
21                 if(s1.charAt(m-1)==s3.charAt(m+n-1)){
22                     match[m][n] |= match[m-1][n];
23                 }
24                 if(s2.charAt(n-1)==s3.charAt(m+n-1)){
25                     match[m][n] |= match[m][n-1];
26                 }
27             }
28             
29         }
30         return match[len1][len2];
31     }
32 }