【LeetCode】Reverse Words in a String III 解题报告

【LeetCode】Reverse Words in a String III 解题报告

标签（空格分隔）： LeetCode

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.

Ways

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。

Date

2017 年 4 月 12 日