题目：

题解：

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        auto f = vector <int> (s2.size() + 1, false);

        int n = s1.size(), m = s2.size(), t = s3.size();

        if (n + m != t) {
            return false;
        }

        f[0] = true;
        for (int i = 0; i <= n; ++i) {
            for (int j = 0; j <= m; ++j) {
                int p = i + j - 1;
                if (i > 0) {
                    f[j] &= (s1[i - 1] == s3[p]);
                }
                if (j > 0) {
                    f[j] |= (f[j - 1] && s2[j - 1] == s3[p]);
                }
            }
        }

        return f[m];
    }
};