leetcode 97 Interleaving String

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        if(s1.size()+s2.size()!=s3.size()) return false;
        int len1=s1.size(),len2=s2.size();
        vector<vector<bool>> dp(len1+1,vector<bool>(len2+1,false));
        dp[0][0]=true;
        for(int i=1;i<=len1;++i) dp[i][0]=dp[i-1][0]&&s1[i-1]==s3[i-1];
        for(int i=1;i<=len2;++i) dp[0][i]=dp[0][i-1]&&s2[i-1]==s3[i-1];
        for(int i=1;i<=len1;++i) {
            for(int j=1;j<=len2;++j) {
                dp[i][j]=(dp[i][j-1]&&s2[j-1]==s3[i+j-1])||(dp[i-1][j]&&s1[i-1]==s3[i+j-1]);
            }
        }
        return dp[len1][len2];
    }
};