LeetCode – Refresh – Interleaving String

Notes:

1. Even s3 is empty string, if s1 and s2 are emtpy, then it should be true.

2. Do not mess up the size of label.

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        int l1 = s1.size(), l2 = s2.size(), l3 = s3.size();
        if (l3 != l2 + l1) return false;
        vector<vector<bool> > dp(l1+1, vector<bool> (l2+1, false));
        dp[0][0] = true;
        for (int i = 1; i <= l1; i++) dp[i][0] = dp[i-1][0] && s1[i-1] == s3[i-1];
        for (int i = 1; i <= l2; i++) dp[0][i] = dp[0][i-1] && s2[i-1] == s3[i-1];
        for (int i = 1; i <= l1; i++) {
            for (int j = 1; j <= l2; j++) {
                dp[i][j] = ((dp[i-1][j] && s1[i-1] == s3[i+j-1]) ||
                            (dp[i][j-1] && s2[j-1] == s3[i+j-1]) ||
                            (dp[i-1][j-1] && s1[i-1] == s3[i+j-1] && s2[j-1] == s3[i+j-2]) ||
                            (dp[i-1][j-1] && s1[i-1] == s3[i+j-2] && s2[j-1] == s3[i+j-1]));
            }
        }
        return dp[l1][l2];
    }
};