LeetCode-in-Java

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 boolean isInterleave(String s1, String s2, String s3) {
        if (s3.length() != (s1.length() + s2.length())) {
            return false;
        }
        Boolean[][] cache = new Boolean[s1.length() + 1][s2.length() + 1];
        return isInterleave(s1, s2, s3, 0, 0, 0, cache);
    }

    public boolean isInterleave(
            String s1, String s2, String s3, int i1, int i2, int i3, Boolean[][] cache) {
        if (cache[i1][i2] != null) {
            return cache[i1][i2];
        }
        if (i1 == s1.length() && i2 == s2.length() && i3 == s3.length()) {
            return true;
        }
        boolean result = false;
        if (i1 < s1.length() && s1.charAt(i1) == s3.charAt(i3)) {
            result = isInterleave(s1, s2, s3, i1 + 1, i2, i3 + 1, cache);
        }
        if (i2 < s2.length() && s2.charAt(i2) == s3.charAt(i3)) {
            result = result || isInterleave(s1, s2, s3, i1, i2 + 1, i3 + 1, cache);
        }
        cache[i1][i2] = result;
        return result;
    }
}

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