【LeetCode】557. Reverse Words in a String III 解题报告(Java & Python)
作者: 负雪明烛
id: fuxuemingzhu
个人博客: http://fuxuemingzhu.cn/
题目地址:https://leetcode.com/problems/reverse-words-in-a-string-iii/#/description
题目描述
Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Example:
Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"
Note:
In the string, each word is separated by single space and there will not be any extra space in the string.
题目大意
把字符串中的每个单词进行翻转,翻转后仍然按照原来的单词顺序进行拼接。
解题方法
Java解法
很简单的题,直接分割开每个单词,然后把单词翻转再拼接就好了。我的第一种做法:
public class Solution {
public String reverseWords(String s) {
String[] words = s.split(" ");
StringBuilder ans = new StringBuilder();
boolean isFirst = true;
for(String word : words){
StringBuilder temp = new StringBuilder(word);
word = temp.reverse().toString();
if(isFirst){
ans.append(word);
isFirst = false;
}else{
ans.append(" " + word);
}
}
return ans.toString();
}
}
看着时间有点长 14 ms,于是没用StringBuilder,方法如下
public class Solution {
public String reverseWords(String s) {
String[] words = s.split(" ");
StringBuilder ans = new StringBuilder();
boolean isFirst = true;
for(String word : words){
word= reverse(word);
if(isFirst){
ans.append(word);
isFirst = false;
}else{
ans.append(" " + word);
}
}
return ans.toString();
}
public String reverse(String s){
char[] chars = s.toCharArray();
for(int i = 0; i < chars.length / 2; i++){
char temp = chars[i];
chars[i] = chars[chars.length - 1 - i];
chars[chars.length - 1 - i] = temp;
}
return new String(chars);
}
}
时间变为 13 ms,还想继续压缩时间。全部用数组实现:
public class Solution {
public String reverseWords(String s) {
String[] words = s.split(" ");
char[] ans = new char[s.length()];
boolean isFirst = true;
int i = 0;
for (String word : words) {
char[] chars = word.toCharArray();
for (int j = 0; j < chars.length / 2; j++) {
char temp = chars[j];
chars[j] = chars[chars.length - 1 - j];
chars[chars.length - 1 - j] = temp;
}
System.arraycopy(chars, 0, ans, i, chars.length);
i += chars.length;
if (i != ans.length) {
ans[i] = ' ';
}
i++;
}
return new String(ans);
}
}
这个时间却变成了16ms,已经无语。嗯。就这样吧。
Python解法
使用Python可以直接使用split函数之后,进行[::-1]即做了翻转操作,然后再用" ".join()拼接在一起就行了。
class Solution(object):
def reverseWords(self, s):
"""
:type s: str
:rtype: str
"""
return " ".join(map(lambda x : x[::-1], s.split(" ")))
日期
2017 年 4 月 12 日
2018 年 11 月 6 日 —— 腰酸背痛要废了
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