Merge Strings Alternatively

Description

Merge Strings Alternately - LeetCode

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.

Examples

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

• $1<=\text{word1.length, word2.length}<=100$
• word1 and word2 consist of lowercase English letters.

Code

class Solution {
public:
    string mergeAlternately(string word1, string word2) {
        string result = "";
        int p1 = 0;
        int p2 = 0;
        size_t s1 = word1.length();
        size_t s2 = word2.length();
 
        while(p1 < s1 || p2 < s2){
            if (p1 < s1){ result += word1[p1]; }
            if (p2 < s2){ result += word2[p2]; }
            p1++;
            p2++;
        }
 
        return result;
    }
};

Approach

1. Create the result variable
2. Create 2 pointers p1, p2 to point at each respective word’s first letter
3. Create 2 sizes s1, s2 to save the function call from calling too many unnecessary functions
4. Loop until neither pointer reached to the end of the word
   1. Check if the first word finished adding to the result
   2. Check if the second word finished adding to the result
   3. Update the pointers
5. Return the result