GoLang: Merge Strings Alternately

You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the other, append the additional letters onto the end of the merged string.

Return the merged string.

Example 1:
Input: word1 = “abc”, word2 = “pqr”
Output: “apbqcr”
Explanation: The merged string will be merged as so:

word1:  a   b   c
word2:    p   q   r
merged: a p b q c r

Example 2:
Input: word1 = “ab”, word2 = “pqrs”
Output: “apbqrs”
Explanation: Notice that as word2 is longer, “rs” is appended to the end.

word1:  a   b 
word2:    p   q   r   s
merged: a p b q   r   s

Example 3:
Input: word1 = “abcd”, word2 = “pq”
Output: “apbqcd”
Explanation: Notice that as word1 is longer, “cd” is appended to the end.

word1:  a   b   c   d
word2:    p   q 
merged: a p b q c   d

Constraints:
1 <= word1.length, word2.length <= 100
word1 and word2 consist of lowercase English letters.

GoLang Algorithm to Merge Strings Alternatively

Let’s keep two pointers, and concatenate characters one by one alternatively from two strings.

func mergeAlternately(word1 string, word2 string) string {
    var l1, l2 = len(word1), len(word2)
    var ans = ""
    for i, j := 0, 0; i < l1 || j < l2; i, j = i + 1, j + 1 {
        if i < l1 {
            ans += string(word1[i])
        }
        if j < l2 {
            ans += string(word2[j])
        }
    }
    return ans
}

GoLang implementation: O(N+M) time where N and M are the lengths of two strings respectively. The space complexity is also O(N+M) as we are allocating a new string (result).

See also: String Interleaving Algorithm

–EOF (The Ultimate Computing & Technology Blog) —