151-Reverse Words in a String

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题意

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.

思路

• 拆成列表，倒序，join
• 去除多个space

class Solution(object):
    def reverseWords(self, s):
        """
        :type s: str
        :rtype: str
        """
        s = s.rstrip()
        s = s.lstrip()
        l = s.split(' ')
        l = l[::-1]
        return ' '.join(i for i in l if i!='' ) # reduce multiple space

分析

• Time: O(n)
• Space: O(n)