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  1. Prepare
  2. Java
  3. Data Structures
  4. Java Stack
  5. Discussions

Java Stack

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641 Discussions

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  • eyha12
     + 0 comments

    Use helper method to check if balanced then return boolean if the stack is empty

    import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner input = new Scanner(System.in); 
        while(input.hasNext()) {
            String line = input.nextLine(); 
            Stack<Character> lineStak = new Stack<>(); 
            for (char chars : line.toCharArray()) {
                if(lineStak.empty()) {
                    lineStak.push(chars); 
                }
                else if (balanced(lineStak.peek(), chars)) lineStak.pop(); 
                else lineStak.push(chars);  
            }
            System.out.println(lineStak.empty());
            
        }
    }
    
    public static boolean balanced(char c1, char c2 ) {
        
        return 
            (c1 == '{' && c2 == '}') ||
            (c1 == '(' && c2 == ')') ||
            (c1 == '[' && c2 == ']')
        ;  
    }
}

  • josegrowl
     + 0 comments

    Simple switch case within a for loop

    import java.util.*;
class Solution{
	
	public static void main(String []argh)
	{
		Scanner sc = new Scanner(System.in);
		
		while (sc.hasNext()) {
			String input=sc.next();
            //Complete the code
            System.out.println(isBalanced(input));
		}
		
	}
    
    private static boolean isBalanced(String input) {
        if(input.length() == 0) {
            return true;
        }
        Stack<Character> stack = new Stack<>();
        for(Character c: input.toCharArray()) {
            switch(c) {
                case '(' :
                case '{' :
                case '[' :
                    stack.add(c);
                    break;
                case ')' :
                    if (stack.isEmpty() || !stack.pop().equals('('))
                        return false;
                    break;
                case '}' :
                    if (stack.isEmpty() || !stack.pop().equals('{'))
                        return false;
                    break;
                case ']' :
                    if (stack.isEmpty() || !stack.pop().equals('['))
                        return false;
                    break;
                default:
                    return false;
            }
        }
        
        return stack.isEmpty();
    }
}

  • ricardoandreh
     + 0 comments

    Using Deque and Map (Java 15):

    import java.util.Deque;
import java.util.LinkedList;
import java.util.Map;
import java.util.Scanner;

class Solution {

    private static final Map<Character, Character> brackets = Map.of(
        ')', '(',
        '}', '{',
        ']', '['
    );
    
    private static boolean check(String input) {
        Deque<Character> stack = new LinkedList<>();

        for (char c : input.toCharArray()) {
            if (brackets.containsKey(c)) {
                if (stack.isEmpty()) return false;

                if (brackets.get(c) != stack.removeLast()) return false;

                continue;
            }

            stack.add(c);
        }

        return stack.isEmpty();
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        while (sc.hasNext()) {
            boolean isBalanced = check(sc.next());

            System.out.println(isBalanced ? "true" : "false");
        }

        sc.close();
    }
}

  • safal_19_bhardw1
     + 1 comment

    import java.util.*; class Solution{

    public static void main(String []argh)
{
    Scanner sc = new Scanner(System.in);

    while (sc.hasNext()) {
        String input=sc.next();
        //Complete the code

        Stack <Character> s = new Stack<>();
        for(int i = 0 ; i<input.length(); i++)
        {
            char  c = input.charAt(i);

            if(c=='{' || c=='(' ||  c=='[')
            {
                s.push(c);
            }
           else if(s.size()!=0 && ((c=='}' && s.peek()=='{') || (c==')' && s.peek()=='(') || (c==']' && s.peek()=='[')))
           {
            s.pop();
           }
           else{
            s.push(c);
           }

        }
        if(s.size()==0) System.out.println("true");
        else System.out.println("false");
    }

}

    }

  • cesarandresvela1
     + 0 comments

    public static void main(String []argh) { Scanner sc = new Scanner(System.in);

        while (sc.hasNext()) {
        String input=sc.next();
        String[] values = input.split("");
        Stack<String> stack = new Stack<>();
        Map<String, String> chars = new HashMap<>();
        chars.put("(", ")");
        chars.put("{", "}");
        chars.put("[", "]");
        boolean malformed = false;

        for (String value: values){
            if (chars.keySet().contains(value)){
                stack.add(value);
            } else {
                try{
                    String openingChar = stack.pop();
                    if (!chars.get(openingChar).equals(value)){
                        malformed = true;
                    }    
                } catch (EmptyStackException e){
                    malformed = true;
                }

            }
        }
        System.out.println(stack.isEmpty() && !malformed ? "true" : "false");

        //Complete the code
    }

}