手摇算法
手摇算法也可以对字符串进行反转，具体可以查看下面的文章
使用正则表达式
我们得到一个字符串的时候，如果这个字符串中有不止一个的空格进行分割，那么我们可以使用正则表达式的方式来得到这个字符串中的所有单个字符串
// 除去开头和末尾的空白字符 s = s.trim(); // 正则匹配连续的空白字符作为分隔符分割 List<String> wordList = Arrays.asList(s.split("\\s+")); Collections.reverse(wordList); return String.join(" ", wordList);
手写API的方式
下面这种写法如果字符串之间是有多个的空格进行分割，那么只会留下一个空格，此时我们可以使用String.spilt(" ");的方式来进行分割
public static StringBuilder trimSpaces(String s) { int left = 0, right = s.length() - 1; // 去掉字符串开头的空白字符 while (left <= right && s.charAt(left) == ' ') { ++left; } // 去掉字符串末尾的空白字符 while (left <= right && s.charAt(right) == ' ') { --right; } // 将字符串间多余的空白字符去除 StringBuilder sb = new StringBuilder(); while (left <= right) { char c = s.charAt(left); if (c != ' ') { sb.append(c); } else if (sb.charAt(sb.length() - 1) != ' ') { sb.append(c); } ++left; } return sb; }
反转字符串
下面的代码提供了反转字符串的多种方式
package com.leetcode.learn.string.middle; import java.util.Arrays; import java.util.Collections; import java.util.List; /** * @author: 张锦标 * @date: 2023/6/7 9:47 * ReverseWords类 */ public class ReverseWords { //API战神 public static String reverseWords1(String s){ //String[] s1 = s.trim().split(" "); //StringBuilder sb = new StringBuilder(); //for (int i = s1.length-1; i>=0; i--) { // if(s1[i]!=null && !s1[i].equals("")){ // sb.append(s1[i].trim()+" "); // } //} //return sb.toString().trim(); //-------------------------------- // 除去开头和末尾的空白字符 s = s.trim(); // 正则匹配连续的空白字符作为分隔符分割 List<String> wordList = Arrays.asList(s.split("\\s+")); Collections.reverse(wordList); return String.join(" ", wordList); } public static String reverseWords(String s) { StringBuilder sb = trimSpaces(s); // 翻转字符串 reverse(sb, 0, sb.length() - 1); // 翻转每个单词 reverseEachWord(sb); return sb.toString(); } public static StringBuilder trimSpaces(String s) { int left = 0, right = s.length() - 1; // 去掉字符串开头的空白字符 while (left <= right && s.charAt(left) == ' ') { ++left; } // 去掉字符串末尾的空白字符 while (left <= right && s.charAt(right) == ' ') { --right; } // 将字符串间多余的空白字符去除 StringBuilder sb = new StringBuilder(); while (left <= right) { char c = s.charAt(left); if (c != ' ') { sb.append(c); } else if (sb.charAt(sb.length() - 1) != ' ') { sb.append(c); } ++left; } return sb; } public static void reverse(StringBuilder sb, int left, int right) { while (left < right) { char tmp = sb.charAt(left); sb.setCharAt(left++, sb.charAt(right)); sb.setCharAt(right--, tmp); } } public static void reverseEachWord(StringBuilder sb) { int n = sb.length(); int start = 0, end = 0; while (start < n) { // 循环至单词的末尾 while (end < n && sb.charAt(end) != ' ') { ++end; } // 翻转单词 reverse(sb, start, end - 1); // 更新start，去找下一个单词 start = end + 1; ++end; } } public static String reverse(String s){ int n = s.length(); char[] chars = s.toCharArray(); for (int i = 0; i < chars.length/2; i++) { char c = chars[chars.length - i - 1]; chars[chars.length-i-1] = chars[i]; chars[i] = c; } return new String(chars); } public static void main(String[] args) { String s = " the sky is blue"; //System.out.println(reverseWords(s)); StringBuilder sb = new StringBuilder(s); System.out.println(sb.reverse()); System.out.println(reverse(s)); reverse(sb,0,s.length()-1); System.out.println(sb); } }
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