In this example, we are going to see how to check whether a String is a balanced string or not?

Example
Input: ([{}{}{}]{})
Output: Given string is Balanced
Input: {}[}[}}
Output: Given string is Not Balanced

A string is a Balanced String or not?

I am going to solve this problem by using ArrayDeque; we can also use Stack either.

Approach:

  • Here I am sticking to (),[],{} characters, if you wish to have more characters you can free to add these characters into the logic.
  • I am adding all open symbols into an array.
  • Create a Map containing all corresponding open and close symbols.
  • Read String from System.in
  • Loop through each character from the String.
  • Check each character, whether it contained in open symbol array or not. If it does not contain, insert the symbol into it ArrayDequeue (Stores only open symbols).
  • So for a certain point in time, all the open symbols will sit into the ArrayDequeue.
  • Now for closed symbols (else case), pop each element from ArrayDqueue and get the corresponding popped element value from the open_close map. If the map doesn’t contain the value of the popped element, we can say the provided string is not balanced.
  • This loop will go through the end of the string length, so by the end of the loop, ArrayDeque should be empty, as we are popping for each iteration.
  • If it is not empty, we can also say that the provided string is not balanced.
  • Let’s see in practice.

A string is a Balanced String or not?

BalancedString.java
import java.util.*;

public class BalancedString {
    private char smallOpen = '(';
    private char smallClose = ')';

    private char midOpen = '[';
    private char midClose = ']';

    private char bigOpen = '{';
    private char bigClose = '}';

    List<Character> openList = Arrays.asList(smallOpen, midOpen, bigOpen);
    Map<Character, Character> open_closeMap = new HashMap<>();

    {
        open_closeMap.put(smallOpen, smallClose);
        open_closeMap.put(midOpen, midClose);
        open_closeMap.put(bigOpen, bigClose);
    }

    public static void main(String[] args) {
        BalancedString balancedString = new BalancedString();
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter any String..");
        String s = sc.nextLine();
        System.out.println(balancedString.isBalanced(s) ? "Given string is Balanced" : "Given string is Not Balanced");
    }

    public boolean isBalanced(String str) {
        Deque<Character> deque = new ArrayDeque<>();
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (openList.contains(c)) {
                deque.push(c);
            } else {
                if (deque.isEmpty()) {
                    return false;
                }
                char pop = deque.pop();
                if (open_closeMap.get(pop) != c) {
                    return false;
                }
            }
        }
        return deque.isEmpty();
    }
}
Output
([{}{}{}]{})
Given string is Balanced

Happy Learning 🙂

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