151. 反转字符串中的单词

class Solution {
    public String reverseWords(String s) {
        char[] ch = s.toCharArray();
        int fast = 0;
        int slow = 0;
        for(;fast<s.length();fast++){
            if (ch[fast]!=' '){
                if (slow!=0){
                    ch[slow++] = ' ';
                }
                while (fast<s.length() && ch[fast]!=' '){
                    ch[slow] = ch[fast];
                    slow++;
                    fast++;
                }
            }
        }
        String str = String.valueOf(ch);
        String subString = str.substring(0, slow); 
        char[] sub_ch = subString.toCharArray();
        reverse(sub_ch,0,slow-1);
        int fa=0;
        int sl=0;
        for(;fa<sub_ch.length;fa++){
            if(sub_ch[fa]!=' '){
                continue;
            }else{
                reverse(sub_ch,sl,fa-1);
                sl = fa+1;
            }
        }
        reverse(sub_ch,sl,fa-1);
        return new String(sub_ch);
    }

    public void reverse(char[] chr,int i,int j){
        for(;i<j;i++,j--){
            char temp = chr[i];
            chr[i] = chr[j];
            chr[j] = temp;
        }
    }
}

class Solution {
    public String reverseWords(String s) {
        s = s.trim();
        int j=s.length()-1,i=j;
        StringBuilder res = new StringBuilder();
        while(i>=0){
            while(i>=0 && s.charAt(i)!=' ') i--;
            res.append(s.substring(i+1,j+1) + ' ');
            while(i>=0 && s.charAt(i)==' ') i--;
            j = i;
        }

        return res.toString().trim();
    }
}