1768. Merge Strings Alternately¶

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.

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.

Solution: Single Iteration Approach¶

Time Complexity: O(n), where n is the length of the longest string between word1 and word2.
Space Complexity: O(1)
The solution is to iterate over the longest string between word1 and word2 and merge the strings by adding letters in alternating order.

TypeScript

function mergeAlternately(word1: string, word2: string): string {
    if (word1.length <= 0) {
        return word2;
    }

    if (word2.length <= 0) {
        return word1;
    }

    const longest = Math.max(word1.length, word2.length);
    let merged = "";

    for(var i = 0; i < longest; i++) {
        merged += word1[i] || "";
        merged += word2[i] || "";
    }

    return merged;
};