How do I solve the Merge Strings Alternately problem?

Use two pointers to alternately merge characters from each string. When one string is exhausted, append the remaining characters from the longer string.

What is the time complexity of the Merge Strings Alternately problem?

The time complexity is O(m + n), where m and n are the lengths of the two strings.

Can I use more space to solve the Merge Strings Alternately problem?

While you can use extra space, the problem can be solved with O(1) extra space if you directly modify the result string.

What happens if the strings are of different lengths in the Merge Strings Alternately problem?

You append the remaining characters of the longer string after alternating characters from both strings.

How does the two-pointer technique help in the Merge Strings Alternately problem?

The two-pointer technique allows you to efficiently traverse both strings and merge them alternately in linear time.

#1768

Easy

auto_awesome双·指针·invariant

LeetCode 题解工作台

交替合并字符串

给你两个字符串 word1 和 word2 。请你从 word1 开始，通过交替添加字母来合并字符串。如果一个字符串比另一个字符串长，就将多出来的字母追加到合并后字符串的末尾。返回合并后的字符串。示例 1：输入： word1 = "abc", word2 = "pqr" 输出： "apbq…

双指针字符串

题目描述

给你两个字符串 word1 和 word2 。请你从 word1 开始，通过交替添加字母来合并字符串。如果一个字符串比另一个字符串长，就将多出来的字母追加到合并后字符串的末尾。

返回 合并后的字符串 。

示例 1：

输入：word1 = "abc", word2 = "pqr"
输出："apbqcr"
解释：字符串合并情况如下所示：
word1：  a   b   c
word2：    p   q   r
合并后：  a p b q c r

示例 2：

输入：word1 = "ab", word2 = "pqrs"
输出："apbqrs"
解释：注意，word2 比 word1 长，"rs" 需要追加到合并后字符串的末尾。
word1：  a   b 
word2：    p   q   r   s
合并后：  a p b q   r   s

示例 3：

输入：word1 = "abcd", word2 = "pq"
输出："apbqcd"
解释：注意，word1 比 word2 长，"cd" 需要追加到合并后字符串的末尾。
word1：  a   b   c   d
word2：    p   q 
合并后：  a p b q c   d

提示：

1 <= word1.length, word2.length <= 100
word1 和 word2 由小写英文字母组成

lightbulb

解题思路

方法一：直接模拟

我们遍历 word1, word2 两个字符串，依次取出字符，拼接到结果字符串中。Python 代码可以简化为一行。

时间复杂度 $O(m + n)$ ，其中 $m$ 和 $n$ 分别是两个字符串的长度。忽略答案的空间消耗，空间复杂度 $O(1)$ 。

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

speed

复杂度分析

指标	值
时间	O(m + n)
空间	O(1)

psychology

面试官常问的追问

外企场景

question_mark
Candidate understands the two-pointer technique and its application to string manipulation.
question_mark
Candidate can handle edge cases when strings are of different lengths.
question_mark
Candidate implements the solution with optimal space complexity.

warning

常见陷阱

外企场景

error
Forgetting to handle cases where one string is longer than the other.
error
Misusing string indexing, causing out-of-bound errors.
error
Not considering the O(1) space requirement and using extra space unnecessarily.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Handle strings with different character sets (e.g., uppercase letters).
arrow_right_alt
Merge strings with varying characters, such as digits or special symbols.
arrow_right_alt
Extend the pattern to merge more than two strings.

help

常见问题

外企场景

继续练习

#1754 构造字典序最大的合并字符串 #1750 删除字符串两端相同字符后的最短长度 #1813 句子相似性 III