翻转单词顺序列

• 算法：首先将整个句子翻转一遍，然后对每个单词进行翻转
• 需要考虑两种边界情况
  
  • 输入字符串是空字符串
  • 输入的字符串只有一个单词，不需要进行翻转（这种情况更难处理）：使用一个专门检查字符串是否为单个单词的函数即可
• 残留问题：本地能够通过对于输入字符串为”“和” “的输出，OJ上会出现对输入” “的异常java.lang.StringIndexOutOfBoundsException: String index out of range: 3

分析

public class Solution {
    public static String ReverseSentence(String str) {
        if(str.equals(" "))
            return str;
        if(str == null || str == "") //如果是空字符串
            return str;
        int len = str.length();
        char[] chars = str.toCharArray();
        if(checkIfOneWord(chars))
            return str;
        ReverseWord(chars,0,len-1);
        int i = 0;
        int before_blank = 0;
        int next_blank = 0;
        while(i < len){
            if(chars[i] == ' '){
                next_blank = i;
                ReverseWord(chars,before_blank,next_blank-1);
                i++;
                before_blank = i;
            } else{
                i++;
            }

        }
        String result = new String(chars);
        return result;
    }

    public static void ReverseWord(char[] chars, int left, int right){
        while(left < right){
            char tmp = chars[left];
            chars[left] = chars[right];
            chars[right] = tmp;
            left++;
            right--;
        }
    }

    public static boolean checkIfOneWord(char[] chars){
        for(int i=0; i < chars.length; i++){
            if(chars[i] == ' ')
                return false;
        }
        return true;
    }

    public static void main(String[] args){
        String str = "I am a student.";
        String s2 ="Wonderful";
        System.out.println(ReverseSentence(" "));
        System.out.println(ReverseSentence(str));
        System.out.println(ReverseSentence(s2));
    }
}