Interleaving String (C++ code)

LeetCode Interleaving String, Aug 31 '12
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.
思路：用递归超时了，只好用DP，整了个矩阵存结果。
bool isInterleave(string s1, string s2, string s3) {
     if(s1.length() + s2.length() != s3.length()) return false;
     int i, j;
     vector<vector<int> > A(s1.length()+1,vector<int>(s2.length()+1));
     A[0][0] = 1;
     for(i = 1; i < s1.length() + 1; i++){
         if(s1[i-1] == s3[i-1]) A[i][0] = A[i-1][0];
     }
  
    for(j = 1; j < s2.length() + 1; j++){
         if(s2[j-1] == s3[j-1]) A[0][j] = A[0][j-1];
     }

     for(i =1; i < s1.length() + 1; i++ ){
      for(j =1; j < s2.length() + 1; j++){
        if((s1[i-1] == s3[i+j-1] && A[i-1][j] == 1) || (s2[j-1] == s3[i+j-1] && A[i][j-1] == 1) )
           A[i][j] = 1;
        }
    }

   if(A[s1.length()][s2.length()] == 1) return true;
   else return false;
}