RemoveKDigits.java

import java.util.*;
public class RemoveKDigits{
    public static String updatedString(String str, int k){
        Stack<Character> s = new Stack<>();
        for(int i=0;i<str.length();i++){
            while(!s.isEmpty() && k>0 && s.peek()-'0'>str.charAt(i)-'0'){
                s.pop();
                k--;
            }
            s.push(str.charAt(i));
        }
        while(k>0){
            s.pop();
            k--;
        }
        StringBuilder sb = new StringBuilder("");
        while(!s.isEmpty()){
            sb.append(s.peek());
            s.pop();
        }
        sb.reverse();
        while(sb.length()>1 && sb.charAt(0)=='0'){
            sb.deleteCharAt(0);
        }
        return sb.toString();
    }
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter the string: ");
        String str=sc.nextLine();
        System.out.print("Enter the number of digits: ");
        int k=sc.nextInt();
        System.out.println(updatedString(str,k));
    }
}