LeetCode.557.Reverse Words in a String III 反转字符串中的单词 III

题目描述

557 Reverse Words in a String III
https://leetcode-cn.com/problems/reverse-words-in-a-string-iii/
https://leetcode.com/problems/reverse-words-in-a-string-iii/description/

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 1:

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.

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解题过程

这道题一看就想着要用两种方法做，第一种是转为字符数组，完全手动操作，一次遍历，遇到一个单词就调函数逆转，第二种是用java String类操作，先split拆分成单词，然后挨个调方法逆转。

代码如下，手动版调试了几次，String类版还是查着SDK才写完，用到了java8中新增的String.join()方法，还学到了StringBuffer类中就有一个reverse()方法可直接用。

class Solution {
    //手动处理版
    public String reverseWords1(String s) {
        char[] str = s.toCharArray();
        int start=0; //要反转的子串的起始位置
        int length=0; //要反转的子串的长度
        for(int i=0; i<str.length; i++){
            //当前字符非空格，继续往前扫描，同时记录子串长度
            if(str[i] != ' '){
                length++;
            }
            //当前字符为空格，或者是最后一个字符
            if(str[i]==' ' || i==str.length-1){
                if(length>1){//当子串长度大于1时
                    reverse(str, start, start+length-1);//反转子串
                }
                length=0;//长度归零
                start=i+1;//起始位置后移
            }
        }
        return new String(str);
    }

    //反转字符数组str中从start到end的内容
    public char[] reverse(char[] str, int start, int end){
        int i=start, j=end;
        while(i<j){
            char temp=str[i];
            str[i] = str[j];
            str[j] = temp;
            i++;
            j--;
        }
        return str;
    }

    //java方法版
    public String reverseWords(String s) {
        String split[] = s.split(" ",-1);//空格分割字符串，-1会保留空字符串
        for(int i=0; i<split.length; i++){
            StringBuffer stringBuffer = new StringBuffer(split[i]);
            split[i] = stringBuffer.reverse().toString();
        }
        return String.join(" ", split);//空格连接split集合成字符串
    }
}

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GitHub代码

algorithms/leetcode/leetcode/_557_ReverseWordsInString3.java
https://github.com/masikkk/algorithms/blob/master/leetcode/leetcode/_557_ReverseWordsInString3.java

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