LeetCode 151:Reverse Words in a String

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

For example,
Given s = "the sky is blue",
return "blue is sky the".

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

click to show clarification.

Clarification:

 

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Could the input string contain leading or trailing spaces?
  Yes. However, your reversed string should not contain leading or trailing spaces.
• How about multiple spaces between two words?
  Reduce them to a single space in the reversed string.

用栈即可解决，注意前导，尾随空格以及多个空格的问题。用正则表达式匹配多个空格然后用一个空格替换。String的split（“ ”）只能识别一个空格，之后的空格会按照字符串保存。

public class Solution {
    public String reverseWords(String s) {
        s=s.trim();
        s=s.replaceAll("[\\s]+"," ");
        String str[]=s.split(" ");
        Stack<String> sta=new Stack<String>();
        String ans="";
        for(String c:str){
            sta.push(c);
        }
        
        while(!sta.isEmpty()){
           ans=ans+sta.pop()+" ";
        }
        
        return ans.trim();
    }
}

public class StringAPIDemo08{
    public static void main(String args[]){
        String str1 = "hello   world" ;        // 定义字符串,3个空格
        //str1=str1.replaceAll("[\\s]+", " ");
        String s[] = str1.split(" ") ;        // 按空格进行字符串的拆分
        System.out.println(s.length) ;      //s的长度为4，空格包含在了字符串里面。
        for(int i=0;i<s.length;i++){        // 循环输出
            System.out.println(s[i]) ;
        }
    }
};