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题号151

给你一个字符串 s ，请你反转字符串中 单词 的顺序。

单词 是由非空格字符组成的字符串。s 中使用至少一个空格将字符串中的 单词 分隔开。

返回 单词 顺序颠倒且 单词 之间用单个空格连接的结果字符串。

我的解法

暴力解法，先将String转为字符数组，遍历找出空格所在地，然后再倒着将其加入，然后在这个过程中加上各种条件限制

class Solution {public String reverseWords(String s) {char[]arr=s.toCharArray();int count=0;ArrayList<Integer> list=new ArrayList<>();if(arr.length==1)return s;for(int i=0;i<arr.length-1;i++){if(arr[0]!=' '&&count==0){list.add(-1);count++;}if(arr[i]==' '&&arr[i+1]!=' ') {list.add(i);count++;}}ArrayList<String> clist=new ArrayList<>();for(int i=count-1;i>=0;i--) {int j = list.get(i);while (j+1<arr.length&&arr[j+1] != ' ') {clist.add(String.valueOf(arr[j+ 1]));j++;}if(i!=0)clist.add(" ");}String ans="";for(String str:clist){ans+=str;}return ans;}
}

另解：

class Solution {public String reverseWords(String s) {//先删除空格StringBuilder str=delSpace(s);//再反转字符串str.reverse();//再反转子串myreserve(str);return str.toString();//转为string类返回}public  StringBuilder delSpace (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) != ' ')//如果当前字符是空格，且sb中前一个字符不是空格则加入{sb.append(c);}++left;}return sb;}public StringBuilder myreserve(StringBuilder s){int i=0;int j=0;while(j<s.length()){if(s.charAt(j)!=' ')j++;else {myreserve1(s, i, j - 1);j++;i = j;}}//反转最后一个单词myreserve1(s,i,j-1);return s;}public StringBuilder myreserve1(StringBuilder s,int a,int b){int slow=a;int fast=b;while(slow<fast){//反转操作（首尾交换）char tmp=s.charAt(slow);s.setCharAt(slow,s.charAt(fast));s.setCharAt(fast,tmp);slow++;fast--;}return s;}
}

思路：先删除空格，再整个反转，最后逐一反转

再另解

class Solution {public String reverseWords(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;}Deque<String> d = new ArrayDeque<String>();StringBuilder word = new StringBuilder();while (left <= right) {char c = s.charAt(left);if ((word.length() != 0) && (c == ' ')) {// 将单词 push 到队列的头部d.offerFirst(word.toString());word.setLength(0);} else if (c != ' ') {word.append(c);}++left;}d.offerFirst(word.toString());return String.join(" ", d);}
}作者：力扣官方题解
链接：https://leetcode.cn/problems/reverse-words-in-a-string/solutions/194450/fan-zhuan-zi-fu-chuan-li-de-dan-ci-by-leetcode-sol/
来源：力扣（LeetCode）
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用一个双端队列，将字符串依次压入队列的头部即可