翻转单词顺序列

先将每个单词翻转，然后再将整个字符数组翻转

char[] s = {am. I}
每个单词翻转
char[] s = {.ma I}
整个翻转 char[] s = {I am.}

public String ReverseSentence(String str) {
        int n = str.length();
        int i = 0, j = 0;
        char[] s = str.toCharArray();
        while(j <= n){
            if(j == n || s[j] == ' '){
                reverse(s,i,j-1);
                i = j+1;
            }
            j++;
        }
        reverse(s,0,n-1);
        return new String(s);
    }

    public void reverse(char[] s,int i, int j){
        while(i<j)
            swap(s,i++,j--);
    }

    public void swap(char[] s,int i, int j){
        char tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
    }