翻转单词顺序列

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public class Solution {
    public String ReverseSentence(String str) {
        if(str.length()==0){
            return str;
        }
        int start=0;
        int end=0;
        char[] arr=str.toCharArray();
        reverse(arr,0,arr.length-1);
        while(end<=arr.length-1){
            while(end<=arr.length-1 && arr[end]!=' '){
              end++;
            }
            reverse(arr, start, end-1);
            end++;
            start = end;
        }
        return new String(arr);
    }
    public static void reverse(char[] arr,int start,int end){
        while(start<end){
            char temp=arr[start];
            arr[start]=arr[end];
            arr[end]=temp;
            start++;
            end--;
        }    
    }
}

public class Solution {
    public String ReverseSentence(String str) {
        char[] chars = str.toCharArray();
        reverse(chars,0,chars.length - 1);
        int blank = -1;
        for(int i = 0;i < chars.length;i++){
            if(chars[i] == ' '){  
                int nextBlank = i;
                reverse(chars,blank + 1,nextBlank - 1);
                blank = nextBlank;
            }
        }
        reverse(chars,blank + 1,chars.length - 1);//最后一个单词单独进行反转
        return new String(chars);
         
    }
    public void reverse(char[] chars,int low,int high){
        while(low < high){
            char temp = chars[low];
            chars[low] = chars[high];
            chars[high] = temp;
            low++;
            high--;
        }
    }
}