6. 151. Reverse Words in a String

class Solution {
    public String reverseWords(String s) {
        int i=s.length()-1;
        StringBuilder sb = new StringBuilder();
        while(i>=0){

            while(i>=0 && s.charAt(i)==' '){
                i--;
            }
            if(i<0){
                break;
            }
            int j=i;
            while(i>=0 && s.charAt(i)!=' '){
                i--;
            }

            if(sb.length()>0){
                sb.append(" "+s.substring(i+1,j+1));
            }else{
                sb.append(s.substring(i+1,j+1));
            }
        }
        return sb.toString();
        
    }
}