leetcode-151-Reverse-Words-in-a-String

描述

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Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Example 1:

Input: s = "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: s = "  hello world  "
Output: "world hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: s = "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

Example 4:

Input: s = "  Bob    Loves  Alice   "
Output: "Alice Loves Bob"

Example 5:

Input: s = "Alice does not even like bob"
Output: "bob like even not does Alice"

Constraints:

• 1 <= s.length <= 104
• s contains English letters (upper-case and lower-case), digits, and spaces ' '.
• There is at least one word in s.

Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?

分析

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翻转字符串里的单词。

解决方案1（Python）

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调用标准库实现。

class Solution:
    def reverseWords(self, s: str) -> str:
        return " ".join(reversed(s.split()))

解决方案2（Python）

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自己实现去除空格，反转字符串，反转字符串列表。

class Solution:
    
    def trim_spaces(self, s):
        left, right = 0, len(s) - 1
        while left <= right and s[left] == ' ':
            left += 1
        while left <= right and s[right] == ' ':
            right -= 1
        result = []
        while left <= right:
            if s[left] != ' ':
                result.append(s[left])
            elif result[-1] != ' ':
                result.append(s[left])
            left += 1
        return result
    
    def reverseStrList(self, myList, left, right):
        while left < right:
            myList[left], myList[right] = myList[right], myList[left]
            left, right = left + 1, right-1
    
    def reverseAllWord(self, myList):
        myListLen = len(myList)
        start = end = 0
        while start < myListLen:
            while end < myListLen and myList[end] != ' ':
                end += 1
            self.reverseStrList(myList, start, end-1)
            start = end + 1
            end += 1
    
    def reverseWords(self, s: str) -> str:
        noSpacesList = self.trim_spaces(s)
        self.reverseStrList(noSpacesList, 0, len(noSpacesList)-1)
        self.reverseAllWord(noSpacesList)
        return ''.join(noSpacesList)

解决方案2 (Golang)

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import "strings"

func reverseWords(s string) string {
    stringList := strings.Fields(s)
    reverseStringList(&stringList, 0, len(stringList)-1)
    return strings.Join(stringList, " ")
}

func reverseStringList(strList *[]string, i int, j int) {
    for i <= j {
        (*strList)[i], (*strList)[j] = (*strList)[j], (*strList)[i]
        i++
        j--
    }
}

相关问题

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• (M) Reverse Words in a String II

题目来源