LeetCode in Net

97. Interleaving String

Medium

Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2.

An interleaving of two strings s and t is a configuration where they are divided into non-empty substrings such that:

• s = s1 + s2 + ... + sn
• t = t1 + t2 + ... + tm
• |n - m| <= 1
• The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ...

Note: a + b is the concatenation of strings a and b.

Example 1:

Input: s1 = “aabcc”, s2 = “dbbca”, s3 = “aadbbcbcac”

Output: true

Example 2:

Input: s1 = “aabcc”, s2 = “dbbca”, s3 = “aadbbbaccc”

Output: false

Example 3:

Input: s1 = “”, s2 = “”, s3 = “”

Output: true

Constraints:

• 0 <= s1.length, s2.length <= 100
• 0 <= s3.length <= 200
• s1, s2, and s3 consist of lowercase English letters.

Follow up: Could you solve it using only O(s2.length) additional memory space?

Solution

public class Solution {
    public bool IsInterleave(string s1, string s2, string s3) {
        if (s1.Length + s2.Length != s3.Length) {
            return false;
        }
        bool[,] dp = new bool[s1.Length + 1, s2.Length + 1];
        dp[0, 0] = true;
        for (int i = 0; i <= s1.Length; i++) {
            for (int j = 0; j <= s2.Length; j++) {
                if (i == 0 && j == 0) {
                    continue;
                }
                if (i > 0 && s1[i - 1] == s3[i + j - 1]) {
                    dp[i, j] |= dp[i - 1, j];
                }
                if (j > 0 && s2[j - 1] == s3[i + j - 1]) {
                    dp[i, j] |= dp[i, j - 1];
                }
            }
        }
        return dp[s1.Length, s2.Length];
    }
}

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