Merge Strings Alternately
(#1768), Easy
Category: String, Two Pointer
Problem Statement
You are given two strings `word1` and `word2`. Merge the strings by adding letters in alternating order, starting with `word1`. If one string is longer than the other, append the additional letters at the end of the merged string. Return the merged string.
Examples
Input: word1 = "abc", word2 = "pqr"
Output: "apbqcr"
Explanation: Characters are alternated: a (from word1), p (from word2), b, q, c, r.
Input: word1 = "ab", word2 = "pqrs"
Output: "apbqrs"
Explanation: After alternating a-p, b-q, word2 has extra characters r and s which are appended.
Input: word1 = "abcd", word2 = "pq"
Output: "apbqcd"
Explanation: After alternating a-p, b-q, word1 has extra characters c and d which are appended.
Approach
Two Pointer Technique
- Initialize two pointers `w1Index` and `w2Index` to 0.
- While both pointers are within bounds of `word1` and `word2`, alternately append one character from each string to the result.
- After the main loop, if there are any remaining characters in `word1` or `word2`, append them to the result string.
- Return the final merged result string.
var mergeAlternately = function (word1, word2) {
let w1Index = 0;
let w2Index = 0;
let s = "";
while (w1Index < word1.length && w2Index < word2.length) {
s += word1[w1Index++];
s += word2[w2Index++];
}
while (w1Index < word1.length) {
s += word1[w1Index++];
}
while (w2Index < word2.length) {
s += word2[w2Index++];
}
return s;
};Complexity
Time: O(n)
Space: O(1) (excluding output string)