97.cpp

// dp.cpp
class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        int n1 = s1.size(), n2 = s2.size(), n3 = s3.size();
        if (n1 + n2 != n3)
            return 0;
        vector<vector<bool>> dp(n1 + 1, vector<bool>(n2 + 1, 0));
        dp[0][0] = 1;
        for (int i = 0; i <= n1; ++i)
            for (int j = 0; j <= n2; ++j)
                if (i > 0 && dp[i - 1][j])
                    dp[i][j] = s3[i + j - 1] == s1[i - 1];
                else if (j > 0 && dp[i][j - 1] && dp[i][j] != 1)
                    dp[i][j] = s3[i + j - 1] == s2[j - 1];
        return dp[n1][n2];
    }
};
// TLE_dfs.cpp
class Solution2 {
    bool impl(string_view s1, string_view s2, string_view s3) {
        if (s1.size() == 0 && s2.size() == 0)
            return true;
        if (s1.size() && s1[0] == s3[0] && impl(s1.substr(1), s2, s3.substr(1)))
            return true;
        if (s2.size() && s2[0] == s3[0] && impl(s1, s2.substr(1), s3.substr(1)))
            return true;
        return false;
    }

public:
    bool isInterleave(string s1, string s2, string s3) {
        if (s1.size() + s2.size() != s3.size())
            return false;
        return impl(s1, s2, s3);
    }
};