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Formatted question description: https://leetcode.ca/all/1768.html

1768. Merge Strings Alternately

Level

Easy

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

Merge the two strings as long as both strings have remaining letters. When a string does not have remaining letters, append the remaining letters of the other string to the merged string.

  • class Solution {
    public String mergeAlternately(String word1, String word2) {
        StringBuffer sb = new StringBuffer();
        int length1 = word1.length(), length2 = word2.length();
        int index1 = 0, index2 = 0;
        while (index1 < length1 && index2 < length2) {
            sb.append(word1.charAt(index1++));
            sb.append(word2.charAt(index2++));
        }
        while (index1 < length1)
            sb.append(word1.charAt(index1++));
        while (index2 < length2)
            sb.append(word2.charAt(index2++));
        return sb.toString();
    }
}

  • // OJ: https://leetcode.com/problems/merge-strings-alternately/
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    string mergeAlternately(string a, string b) {
        int i = 0, j = 0, M = a.size(), N = b.size();
        string ans;
        while (i < M || j < N) {
            if (i < M) ans += a[i++];
            if (j < N) ans += b[j++];
        }
        return ans;
    }
};

  • class Solution:
    def mergeAlternately(self, word1: str, word2: str) -> str:
        return ''.join(a + b for a, b in zip_longest(word1, word2, fillvalue=''))

############

class Solution:
    def mergeAlternately(self, word1: str, word2: str) -> str:
        cur1 = 0
        cur2 = 0
        res = ""
        while cur1 < len(word1) and cur2 < len(word2):
            res += word1[cur1] + word2[cur2]
            cur1 += 1
            cur2 += 1
        if cur1 != len(word1):
            res += word1[cur1:]
        if cur2 != len(word2):
            res += word2[cur2:]
        return res

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