BalancedParentheses.java

package com.examplehub.datastructures.stack;

import java.util.Stack;

public class BalancedParentheses {

  /**
   * Test if a parentheses expression
   *
   * @param parenthesesExpr the parentheses expression
   * @return {@code true} if given parentheses expression is balanced.å
   */
  public static boolean isBalanced(String parenthesesExpr) {
    Stack<Character> stack = new Stack<>();
    for (int i = 0; i < parenthesesExpr.length(); i++) {
      switch (parenthesesExpr.charAt(i)) {
        case '(':
        case '[':
        case '{':
          stack.push(parenthesesExpr.charAt(i));
          break;
        case ')':
        case ']':
        case '}':
          if (stack.isEmpty() || !isPaired(stack.pop(), parenthesesExpr.charAt(i))) {
            return false;
          }
      }
    }
    return stack.isEmpty();
  }

  /**
   * Test if left bracket and right bracket is paired.
   *
   * @param leftBracket the left bracket.
   * @param rightBracket the right bracket.
   * @return {@code true} if two brackets are paired.
   */
  public static boolean isPaired(char leftBracket, char rightBracket) {
    return leftBracket == '(' && rightBracket == ')'
        || leftBracket == '[' && rightBracket == ']'
        || leftBracket == '{' && rightBracket == '}';
  }
}