class Solution {public:    bool isInterleave(string s1, string s2, string s3) {        //if (s1 == "" && s2 == "" && s3 == "") return true;        //if (s1 == "" || s2 == "" || s3 == "") return false;        if (s1.length() + s2.length() != s3.length()) return false;                vector
    
     
      > match(s1.length()+1, vector
      
       (s2.length()+1, false));        match[0][0] = true;                for (int idx = 0; idx < s1.length() + s2.length(); ++idx) {            for (int s1Len = 0; s1Len <= idx+1 && s1Len <= s1.length(); ++s1Len) {                int s2Len = idx + 1 - s1Len;                if (s2Len > s2.length()) continue;                if ((s1Len > 0 && match[s1Len-1][s2Len] && s3[idx] == s1[s1Len-1]) ||                    (s2Len > 0 && match[s1Len][s2Len-1] && s3[idx] == s2[s2Len-1]))                    match[s1Len][s2Len] = true;            }        }                return match[s1.length()][s2.length()];    }};