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

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645 Discussions

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  • alflop00
     + 0 comments

    import java.util.*; class Solution{

    public static void main(String []argh)
{
    Scanner sc = new Scanner(System.in);
    List<String> input = new ArrayList<>();
    while (sc.hasNext()) {
        input.add(sc.next());
    }

          List<Stack<Character>> stacks = new ArrayList<>();

          for(String st : input)
          {    Stack<Character> characters = new Stack<>();
               for (char ch : st.toCharArray()) 
               {
                   characters.push(ch);
               }
               stacks.add(characters);
          }

       for(Stack stk : stacks)
       {
         int a = 0;
         int b = 0;
         int c = 0;
         for(int i = stk.size() -1; i > -1 ; i--) 
         {
          Character ch = (Character) stk.elementAt(i);   
          if((ch == '(' ))
           {   
               stk.pop();
               a++;
           }
           if((ch == ')' ))
           {   
               stk.pop();
               if(a == 1){
                a = 3;
               }
               a--;
           }
            if((ch == '[' ))
           {   
               stk.pop();
               if(b == 1){
                a = 3;
               }
               b++;
           }
           if((ch == ']' ))
           {   
               stk.pop();
               if(b == 1){
                b = 3;
               }
               b--;
           }
           if((ch == '{' ))
           {   
               stk.pop();
               c++;
           }
           if((ch == '}' ))
           {   
               stk.pop();
               if(c == 1){
                c = 3;
               }
               c--;
           }
    }
    System.out.println(((a+b+c) == 0)? true : false);
  }
}

    }

  • sujaldaware7721
     + 1 comment

    class Solution{

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

    while (sc.hasNext()) {
     String s = sc.nextLine();
     int n = s.length();
     int counter = 0;
     int counter1 = 0;
     if(s.startsWith("}") || s.startsWith("]") || s.startsWith(")")){
        System.out.println("false");
     }else if(s.endsWith("(") || s.endsWith("{") || s.endsWith("[")){
         System.out.println("false");
     }else {

        for (int i = 0; i < n; i++) {
            if (s.charAt(i) == '(' || s.charAt(i) == '[' || s.charAt(i) == '{') {
                counter++;
            }
            if (s.charAt(i) == ')' || s.charAt(i) == ']' || s.charAt(i) == '}') {
                counter1++;
            }
        }
        if (counter == counter1) {
          System.out.println("true");
        } else {
          System.out.println("false");
        }
    }
 }

    } }

  • somya_garg2906
     + 0 comments

    A solution without using stack -

    import java.util.*; class Solution{

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

    while (sc.hasNext()) {
        String input=sc.next();
        int count = 0;
        //Complete the code
        if (input.length() % 2 == 0){
           for (int i = 0 ; i < input.length(); i++){
                if (input.charAt(i) == '{' ||
                    input.charAt(i) == '[' ||
                    input.charAt(i) == '('){
                    count+=1;
                }
                else{
                    count-=1;
                }
                if(count < 0){
                    System.out.println("false");
                    break;
                }
            } 
            if (count == 0){
                System.out.println("true");
            }
        }
        else {
            System.out.println("false");
        }

    }

}

    }

  • jhoneder
     + 0 comments
    import java.util.Scanner;
import java.util.Stack;

public class Solution {

    private static final char KEY_OPENS_BRACKET = '{';
    private static final char KEY_CLOSES_BRACKET = '}';
    private static final char PARENTHESIS_OPENS_BRACKET = '(';
    private static final char PARENTHESIS_CLOSES_BRACKET = ')';
    private static final char SQUARE_PARENTHESIS_OPENS_BRACKET = '[';
    private static final char SQUARE_PARENTHESIS_CLOSES_BRACKET = ']';

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

        while(scanner.hasNext()){
            Stack<Character> stack = new Stack<>();
            String input = scanner.nextLine();
            System.out.println(isValid(input, stack));
        }
        scanner.close();
    }

    private static boolean isValid(String input, Stack<Character> stack) {
        for(char chr : input.toCharArray()) {
            if(isOpenBracket(chr)) {
                stack.push(chr);
                continue;
            }
            if(chr == KEY_CLOSES_BRACKET  && !stack.isEmpty() && stack.peek() == KEY_OPENS_BRACKET) {
                stack.pop();
                continue;
            }
            if(chr == PARENTHESIS_CLOSES_BRACKET && !stack.isEmpty() && stack.peek() == PARENTHESIS_OPENS_BRACKET) {
                stack.pop();
                continue;
            }
            if (chr == SQUARE_PARENTHESIS_CLOSES_BRACKET &&!stack.isEmpty() && stack.peek() == SQUARE_PARENTHESIS_OPENS_BRACKET) {
                stack.pop();
                continue;
            }
            if (isCloseBracket(chr)) {
                stack.push(chr);
                break;
            }
        }
        return stack.isEmpty();
    }

    private static boolean isOpenBracket(char chr) {
        return switch (chr) {
            case KEY_OPENS_BRACKET, PARENTHESIS_OPENS_BRACKET, SQUARE_PARENTHESIS_OPENS_BRACKET -> true;
            default -> false;
        };
    }

    private static boolean isCloseBracket(char chr) {
        return switch (chr) {
            case KEY_CLOSES_BRACKET, PARENTHESIS_CLOSES_BRACKET, SQUARE_PARENTHESIS_CLOSES_BRACKET -> true;
            default -> false;
        };
    }
}

  • 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 == ']')
        ;  
    }
}