leetcode[97]Interleaving String

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        if(s1.size()+s2.size()!=s3.size())return false;
        vector<vector<bool>> f(s1.size()+1,vector<bool> (s2.size()+1,false));
        f[0][0]=true;
        for(int i=1;i<=s1.size();i++)
        {
            f[i][0]=(f[i-1][0]&&s1[i-1]==s3[i-1]);
        }
        for(int j=1;j<=s2.size();j++)
        {
            f[0][j]=(f[0][j-1]&&s2[j-1]==s3[j-1]);
        }
        for(int i=1;i<=s1.size();i++)
        {
            for(int j=1;j<=s2.size();j++)
            {
                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]);
            }
        }
        return f[s1.size()][s2.size()];
    }
};