97.cpp

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        if (s1.size() + s2.size() != s3.size())
            return false; 
        int n1 = s1.size(), n2 = s2.size();
        vector<vector<bool>> dp(n1 + 1, vector<bool> (n2 + 1));  
        dp[0][0] = true;
        for (int i = 1; i <= n1; ++i) {
            dp[i][0] = dp[i - 1][0] && (s1[i - 1] == s3[i - 1]);
        }
        for (int i = 1; i <= n2; i++){
            dp[0][i] = dp[0][i-1] && (s2[i-1] == s3[i-1]);
        }
        for (int i = 1; i <= n1; ++i) {
            for (int j = 1; j <= n2; ++j) {
                dp[i][j] = (dp[i - 1][j] && s1[i - 1] == s3[i - 1 + j]) || (dp[i][j - 1] && s2[j - 1] == s3[j - 1 + i]);
            }
        }
        return dp[n1][n2];
    }
};