交叉合併字串 Merge Strings Alternately_Leetcode 精選75題解析

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題目敘述

題目會給定我們兩個輸入字串word1, word2，要求我們依照word1,word2,word1,word2, ... 交叉前進的方式，合併兩個字串，作為輸出。

題目的原文敘述

測試範例

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

約束條件

Constraints:

• 1 <= word1.length, word2.length <= 100

word1, word2字串長度介於1 ~ 100個字元之間。

• word1 and word2 consist of lowercase English letters.

word1, word2都只會有英文小寫字母。

演算法

建立一個空陣列[]最為暫存buffer，讓word1, word2 依序交叉前進，把每個字元放入這個buffer。

最後，把buffer內的字元合併以字串的形式輸出即可。

程式碼

class Solution:
    def mergeAlternately(self, word1: str, word2: str) -> str:

        a, b =0, 0

        res = []
        while a < len(word1) or b < len(word2):
            if a < len(word1):
                res.append( word1[a] )
                a += 1
            if b < len(word2):
                res.append( word2[b] )
                b += 1
            
        return "".join(res)

額外補充，當我們要把某個容器內的字串作合併輸出時，常常使用"".join( ...容器...)這個語法。

Python official docs about str.join( )

另解，假如已經比較熟悉Python內建函數庫的同學，也可以使用zip搭配generator生成器來依序合併兩個字串。