Cool Dog T questions: padded left bracket (stack)

description:

// Input 1 + 2) * 3-4) * 5-6))) 
// Output ((1 + 2) * ((3-4) * (5-6)))

Code:

import java.util.*;

public class G {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine().trim();
        String result = getfullstr(str);
        System.out.println(result);
    }

    public static String getfullstr(String str) {
        Stack<String> lefts = new Stack<>();
        Stack<String> rights = new Stack<>();
        char[] chars = str.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            char c = chars[i];
            if (c == '+' || c == '-' || c == '+' || c == '*' || c == '/') {
                rights.add(c + "");
            } else if (c == ')') {
                String lstr1 = lefts.pop();
                String lstr2 = lefts.pop();
                String rstr1 = rights.pop();
                lefts.add("(" + lstr2 + rstr1 + lstr1 + ")");
            } else if (Character.isDigit(chars[i])) {
                String num = c + "";
                while ((i + 1) < chars.length && Character.isDigit(chars[i + 1])) {
                    num += c;
                    i++;
                }
                lefts.add(num);
            }
        }
        while (rights.size() > 0) {
            String lstr1 = lefts.pop();
            String lstr2 = lefts.pop();
            String rstr1 = rights.pop();
            lefts.add("(" + lstr2 + rstr1 + lstr1 + ")");
        }
        String result = "";
        while (lefts.size() > 0) {
            result = lefts.pop() + result;
        }
        return result;
    }
}