Merge String 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.

JavaScript

My first thought was a try-catch to read an array then write a new string that failed when we ran out indexes, but using JavaScript, we don’t get an error. Instead of an error, we get an “undefined.” Rather than check for undefined, I used a couple ternary’s and only added to the new word if the index was in range.

/**
 * @param {string} word1
 * @param {string} word2
 * @return {string}
 */
var mergeAlternately = function(word1, word2) {
    let newWord = "";
    let index = 0;
    while ( index < word1.length || index < word2.length ){
        newWord += index < word1.length ? word1[index] : "";
        newWord += index < word2.length ? word2[index] : "";
        index++;
    }
    return newWord;
};

Python

The comments on this LeetCode clued me in to the fact that strings are immutable in Python, and so using += to concatenate strings creates a new string each time. This is not very efficient, and so using join was the recommended solution. Additionally, python does fail when referencing an array index that doesn’t exist, so I implemented the try-catch (try-except) here. Also note, Python uses .append instead of .push for arrays. Here’s an example.

class Solution:
    def mergeAlternately(self, word1: str, word2: str) -> str:
        newWordArray = []
        index = 0
        moreWord1 = True
        moreWord2 = True
        while moreWord1 or moreWord2:
            try:
                newWordArray.append(word1[index])
            except:
                moreWord1 = False
            try:
                newWordArray.append(word2[index])
            except:
                moreWord2 = False
            index += 1
        return "".join(newWordArray)