151. Reverse Words in a String （快慢指针）

Given an input string, reverse the string word by word.

Example:  

Input: "the sky is blue",
Output: "blue is sky the".

Note:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

Follow up: For C programmers, try to solve it in-place in O(1) space.

class Solution:
    def reverseWords(self, s: str) -> str:
        def reverse(word):
            word = list(word)
            n = len(word)
            for i in range((n//2)):
                word[i],word[n-i-1] = word[n-i-1],word[i]
            return ''.join(word)
        s = reverse(s.strip())
        return ' '.join([reverse(w) for w  in s.split()])

 

 

 

 

 

 

/*
 * @lc app=leetcode.cn id=151 lang=cpp
 *
 * [151] 反转字符串中的单词
 */

// @lc code=start
class Solution {
public:
    void reverse(string& s, int ss, int e) {
        int start = ss;
        int end = e;
        while(start<end) {
            char tt = s[start];
            s[start] = s[end];
            s[end] = tt;
            start++;
            end--;
        }
    }
    string reverseWords(string s) {
        // del space
        int a = 0;
        for(int i = 0;i < s.size();i++) {
            if ((s[i] != ' ') || (s[i] == ' ' && i-1>=0 && s[i-1] !=' ')) {
                s[a] = s[i];
                a++;
            }
        }
        // del last space
        if (s[a-1] == ' ') {
            s.resize(a-1);
        } else {
            s.resize(a);
        }
        
        reverse(s,0,s.size()-1);
        int k = 0;
        for(int i = 0; i < s.size(); i++) {
            if (s[i]==' ') {
                reverse(s,k,i-1);
                k = i+1;
            }
        }
        // reverse last word
        reverse(s,k,s.size()-1);
        return s;
    }
};
// @lc code=end

 

 

class Solution {
public:
    //[]
    void reverse(string& s, int start, int end) {
        int i = start,j = end;
        while(i<j) {
            char tt = s[i];
            s[i] = s[j];
            s[j] = tt;
            i++;j--;
        }
    }
    string reverseWords(string s) {
        
        // 删除空格
        int a = 0;
        for(int j = 0;j < s.size();j++) {
            if (s[j]!=' ') {
                if (a!=0) s[a++] = ' ';
                while(j < s.size() && s[j]!=' ') s[a++] = s[j++];
            }
        }
        s.resize(a);
        // 先整体反转字符串
        reverse(s,0,s.size()-1);
        int i = 0;
        
        // 每个字符串再反转
        for(int j = 0;j < s.size();j++) {
            if (s[j]==' ') {
                reverse(s,i,j-1);
                i = j+1;
            }
        }
        reverse(s,i,s.size()-1);
        
        return s;
    }
};

 

 

 

 

 

 

class Solution(object):
    def reverseWords(self, s):
        """
        :type s: str
        :rtype: str
        """
        return ' '.join(s.strip().split()[::-1])