LeetCode: 151. Reverse Words in a String 翻转字符串中的词

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本文介绍了一种将字符串按单词进行反转的方法，并提供了多个示例代码实现。通过对输入字符串中单词的处理，确保反转后的字符串既没有前导也没有尾随空格，并且单词之间的多余空格被压缩为单个空格。

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

Example 1:

Input: “the sky is blue”
Output: “blue is sky the”
Example 2:

Input: " hello world! "
Output: “world! hello”
Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:

Input: “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.

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.
代码：

class Solution {
    public String reverseWords(String s) {
        if(s == null || s.length() == 0) return s;
        
        String[] sArr = s.trim().split(" ");
        StringBuilder temp = new StringBuilder();
        for(int i = sArr.length-1; i >= 0; i--){
            if(sArr[i] == null || sArr[i].equals("")) continue;
            temp.append(sArr[i]);
            temp.append(" ");
        }
        if(temp.length() > 0)
            temp.deleteCharAt(temp.length()-1);
        return temp.toString();
    }
}

class Solution {
    public String reverseWords(String s) {
        StringBuilder out = new StringBuilder();
        if(s==null || s.length()==0) return "";
        
        s = s.trim();
        String tmp = "";
        for(int i=s.length()-1; i>=0; i--){
            char t = s.charAt(i);
            if(t==' '){
                while(i-1>=0 && s.charAt(i-1)==' ') i--;
                out.append(tmp+" ");
                tmp = "";
            }else{
                tmp = t + tmp;
            }
        }
        out.append(tmp);
        
        return out.toString();
    }
}

public String reverseWords(String s) {
        StringBuilder sb = new StringBuilder();
        int i = s.length() - 1;
        while(i >= 0){
            if(s.charAt(i) == ' '){
                i--;
                continue;
            }
            int start = s.lastIndexOf(' ', i);
            sb.append(' ');
            sb.append(s.substring(start + 1, i + 1));
            i = start - 1;
        }
        if(sb.length() > 0){
            sb.deleteCharAt(0);    
        }
        
        return sb.toString();
        
    }

翻转https://www.baidu.com成com.baidu.www://https：

public class Main{
    public static void main(String[] args){
        String in = "https://www.baidu.com";
        Main main = new Main();
        System.out.println(main.split(in));
        System.out.println(main.split2(in));
        System.out.println(main.split3(in));
    }

    private String split(String in){
        if(in==null || in.length()==0) return "";
        StringBuilder ss = new StringBuilder();
        int end = in.length()-1;
        while(end>=0){
            int start = in.lastIndexOf(".",end);
            if(start!=-1){
                ss.append("."+in.substring(start+1,end+1));
            }else{
                start = in.lastIndexOf("://", end);
                if(start!=-1){
                    ss.append("."+in.substring(start+3,end+1));
                }else{
                    ss.append("://"+in.substring(start+1,end+1));
                }
            }
            end = start-1;
        }
        ss.deleteCharAt(0);
        return ss.toString();
    }

    private String split2(String in){
        String[] strs = in.split("\\.");
        StringBuilder out = new StringBuilder();
        for(int i=strs.length-1; i>=0; i--){
            if(i!=0){
                out.append(strs[i]);
                out.append(".");
            }else{
                String[] tmp = strs[i].split("://");
                out.append(tmp[1]);
                out.append("://");
                out.append(tmp[0]);
            }
        }
        return out.toString();
    }
    private String split3(String in){
        String[] strs = in.split("\\.|(://)");
        StringBuilder out = new StringBuilder();
        for(int i=strs.length-1; i>=0; i--){
            if(i!=0){
                out.append(strs[i]);
                out.append(".");
            }else{
                out.deleteCharAt(out.length()-1);
                out.append("://");
                out.append(strs[i]);
            }
        }
        return out.toString();
    }
}