力扣dp

97.

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        int len1 = s1.length(), len2 = s2.length(), len3 = s3.length();
        if (len3 != len1 + len2)
            return false;
        if (len1 == 0 and s2 == s3 or len2 == 0 and s1 == s3)
            return true;
        if (len1 == 0 and len2 == 0 and len3 == 0)
            return true;
        vector<vector<int> >dp(len1 + 1, vector<int>(len2 + 1, 0));
        for (int i = 0; i <= len1; ++i) {
            for (int j = 0; j <= len2; ++j) {
                if (i == 0 and j == 0) {
                    dp[0][0] = 1;
                    continue;
                }
                if (j > 0 and s3[i + j - 1] == s2[j - 1])
                    dp[i][j] |= dp[i][j - 1];
                if (i > 0 and s3[i + j - 1] == s1[i - 1])
                    dp[i][j] |= dp[i - 1][j];
            }
        }
        return dp[len1][len2];
    }
};