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.

public class Solution {
public boolean isInterleave(String s1, String s2, String s3) {
// Start typing your Java solution below
// DO NOT write main() function
int n1 = s1.length();
int n2 = s2.length();
int n3 = s3.length();
if(n1 + n2 != n3)
return false;
boolean[][] ans = new boolean[n1 + 1][n2 + 1];
// ans[i][j] == true means s3.substring(0, i + j) is an interleaving string
ans[0][0] = true;
for(int i = 1; i <= n1; i++){
if(s1.charAt(i - 1) == s3.charAt(i - 1))
ans[i][0] = true;
else
break;
}
for(int i = 1; i <= n2; i++){
if(s2.charAt(i - 1) == s3.charAt(i - 1))
ans[0][i] = true;
else
break;
}
for(int i = 1; i <= n1; i++){
for(int j = 1; j <= n2; j++){
if(s1.charAt(i - 1) == s3.charAt(i + j - 1))
ans[i][j] = ans[i][j] || ans[i - 1][j];
if(s2.charAt(j - 1) == s3.charAt(i + j - 1))
ans[i][j] = ans[i][j] || ans[i][j - 1];
}
}
return ans[n1][n2];
}
}