1768. Merge Strings Alternately

1. Description

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.

2. Example

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

3. Constraints

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

4. Solutions

Two Pointers

Time complexity: O(n)
Space complexity: O(n)

class Solution {
public:
    string mergeAlternately(const string &word1, const string &word2) {
        string result;
        result.reserve(word1.size() + word2.size());
        for (int i = 0; i < word1.size() || i < word2.size(); ++i) {
            if (i < word1.size()) {
                result.push_back(word1[i]);
            }
            if (i < word2.size()) {
                result.push_back(word2[i]);
            }
        }

        return result;
    }
};