Check balanced parentheses in a string

Given a string with parentheses (round brackets) and letters, validate the parentheses:
1. An opening parentheses '(' should have a closing matching parentheses ')'.
2. Closing matching parentheses should not come before an opening parentheses.
Note: Assume that the string has alphabets and numbers and round brackets only.

For example:
((BCD)AE) - Valid
)(PH)N(X) - Invalid

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1. Iterate over the string.
2. Create count = 0, increment count if an opening parentheses is seen, decrement count if a closing parentheses is seen.
3. If when a closing parentheses is seen and count is 0, then it means that the current closing parentheses does not have a matching opening parentheses, so return false.
4. When iteration completes, if count is not 0, it means there is an opening parentheses without a matching closing parentheses, so return false.
5. If count is 0, return true.

We will create a separate post for validating an expression having multiple types of parentheses (round brackets (), curly brackets {}, square brackets [] etc)

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Algorithm Visualization

Code Snippet

package com.ideserve.questions.saurabh;

 * <b>IDeserve <br>
 * <a href=""></a>
 * Given a string with parentheses (round brackets) and letters, validate the parentheses.
 * @author Saurabh
public class Parentheses {

	public static boolean isValid(String str) {

		if (str == null || str.length() == 0) {
			return true;

		int count = 0;
		int i = 0;
		while (i < str.length()) {
			char ch = str.charAt(i);
			if (ch == '(') {
			} else if (ch == ')') {
				if (count == 0)
					return false;

		if(count != 0) 
			return false;
		return true;
	public static void main(String[] args) {
		String str = "((BCD)AE)";
		System.out.println("isValid: " + isValid(str));
		str = ")(PH)N(X)";
		System.out.println("isValid: " + isValid(str));

Order of the Algorithm

Time Complexity is O(n)
Space Complexity is O(1)


  • Sincere thanks from IDeserve community to Saurabh Kumar for compiling current post.

    Saurabh Kumar

    Ninja Programmer