151. Reverse Words in a String-------

class Solution {
    public String reverseWords(String s) {
        //use trim() for removing extra space
        s = s.trim();
        //creat Stack<String> for storing word
        Stack<String> stack = new Stack<>();
        int j = 0;
        //using for loop for iterating String s
        for(int i=1; i<s.length(); i++){
            //base case
            if(s.charAt(i) == ' ' && s.charAt(i-1) != ' '){
                stack.push(s.substring(j,i).trim());
                j = i + 1;
            }
        }
        //append the substring
        stack.push(s.substring(j));

        //create StringBuilder to store reversed value
        StringBuilder sb = new StringBuilder();

        while(!stack.isEmpty()) {
            sb.append(stack.pop()).append(" ");
        }

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