LeetCode-in-Go

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 s and t are divided into n and m non-empty substrings respectively, 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

Explanation: One way to obtain s3 is: Split s1 into s1 = “aa” + “bc” + “c”, and s2 into s2 = “dbbc” + “a”. Interleaving the two splits, we get “aa” + “dbbc” + “bc” + “a” + “c” = “aadbbcbcac”. Since s3 can be obtained by interleaving s1 and s2, we return true.

Example 2:

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

Output: false

Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3.

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

func isInterleave(s1 string, s2 string, s3 string) bool {
	if len(s3) != len(s1)+len(s2) {
		return false
	}
	cache := make([][]*bool, len(s1)+1)
	for i := range cache {
		cache[i] = make([]*bool, len(s2)+1)
	}
	return isInterleaveHelper(s1, s2, s3, 0, 0, 0, cache)
}

func isInterleaveHelper(s1, s2, s3 string, i1, i2, i3 int, cache [][]*bool) bool {
	if cache[i1][i2] != nil {
		return *cache[i1][i2]
	}
	if i1 == len(s1) && i2 == len(s2) && i3 == len(s3) {
		return true
	}
	result := false
	if i1 < len(s1) && s1[i1] == s3[i3] {
		result = isInterleaveHelper(s1, s2, s3, i1+1, i2, i3+1, cache)
	}
	if i2 < len(s2) && s2[i2] == s3[i3] {
		result = result || isInterleaveHelper(s1, s2, s3, i1, i2+1, i3+1, cache)
	}
	cache[i1][i2] = &result
	return result
}

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