class Solution {public:    bool isInterleave(string s1, string s2, string s3) {        int n1 = s1.length(), n2 = s2.length(), n3 = s3.length();        if (n1+n2 != n3) return false;        vector<vector<bool>> V(n1+1, vector<bool>(n2+1, false));        V[n1][n2] = (s3[n1+n2]==‘\0‘);        // fill bottom        for (int j=n2-1; j>=0; j--) V[n1][j]  = (s2[j]==s3[n1+j] && V[n1][j+1]);        // fill right        for (int i=n1-1; i>=0; i--) V[i][n2] = (s1[i]==s3[n2+i] && V[i+1][n2]);        // fill DP table from bottom right        for (int j=n2-1; j>=0; j--){            for (int i=n1-1; i>=0; i--){                V[i][j] = (s1[i]==s3[i+j] && V[i+1][j]) | (s2[j]==s3[i+j] && V[i][j+1]);            }        }        return V[0][0];    }};