[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.

DP.

 1 class Solution {
 2 private:
 3     bool f[1000][1000];
 4 public:
 5     bool isInterleave(string s1, string s2, string s3) {
 6         // Start typing your C/C++ solution below
 7         // DO NOT write int main() function 
 8         if (s1.size() + s2.size() != s3.size())
 9             return false;
10             
11         f[0][0] = true;
12         for(int i = 1; i <= s1.size(); i++)
13             f[i][0] = f[i-1][0] && (s3[i-1] == s1[i-1]);
14             
15         for(int j = 1; j <= s2.size(); j++)
16             f[0][j] = f[0][j-1] && (s3[j-1] == s2[j-1]);
17             
18         for(int i = 1; i <= s1.size(); i++)
19             for(int j = 1; j <= s2.size(); j++)
20                 f[i][j] = (f[i][j-1] && s2[j-1] == s3[i+j-1]) || (f[i-1][j] && s1[i-1] == s3[i+j-1]);
21                 
22         return f[s1.size()][s2.size()];
23     }
24 };