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Jul 8, 2025
Merged

refactor: optimize ValidParentheses methods and add parameterized tests #6352

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6d8f87b
refactor: optimize ValidParentheses methods and add parameterized tests
alxkm Jul 7, 2025
cc6e0e1
refactor: fix clang formatting issues
alxkm Jul 7, 2025
2588cdc
refactor: fix spotbugs issue
alxkm Jul 7, 2025
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84 changes: 39 additions & 45 deletions src/main/java/com/thealgorithms/strings/ValidParentheses.java
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Original file line number Diff line number Diff line change
@@ -1,59 +1,53 @@
package com.thealgorithms.strings;
// Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine
// if the input string is valid. An input string is valid if: Open brackets must be closed by
// the same type of brackets. Open brackets must be closed in the correct order. Every close
// bracket has a corresponding open bracket of the same type.

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Map;

/**
* Validates if a given string has valid matching parentheses.
* <p>
* A string is considered valid if:
* <ul>
* <li>Open brackets are closed by the same type of brackets.</li>
* <li>Brackets are closed in the correct order.</li>
* <li>Every closing bracket has a corresponding open bracket of the same type.</li>
* </ul>
*
* Allowed characters: '(', ')', '{', '}', '[', ']'
*/
public final class ValidParentheses {
private ValidParentheses() {
}

private static final Map<Character, Character> BRACKET_PAIRS = Map.of(')', '(', '}', '{', ']', '[');

/**
* Checks if the input string has valid parentheses.
*
* @param s the string containing only bracket characters
* @return true if valid, false otherwise
* @throws IllegalArgumentException if the string contains invalid characters or is null
*/
public static boolean isValid(String s) {
char[] stack = new char[s.length()];
int head = 0;
if (s == null) {
throw new IllegalArgumentException("Input string cannot be null");
}

Deque<Character> stack = new ArrayDeque<>();

for (char c : s.toCharArray()) {
switch (c) {
case '{':
case '[':
case '(':
stack[head++] = c;
break;
case '}':
if (head == 0 || stack[--head] != '{') {
return false;
}
break;
case ')':
if (head == 0 || stack[--head] != '(') {
return false;
}
break;
case ']':
if (head == 0 || stack[--head] != '[') {
if (BRACKET_PAIRS.containsValue(c)) {
stack.push(c); // opening bracket
} else if (BRACKET_PAIRS.containsKey(c)) {
if (stack.isEmpty() || stack.pop() != BRACKET_PAIRS.get(c)) {
return false;
}
break;
default:
throw new IllegalArgumentException("Unexpected character: " + c);
}
}
return head == 0;
}
public static boolean isValidParentheses(String s) {
int i = -1;
char[] stack = new char[s.length()];
String openBrackets = "({[";
String closeBrackets = ")}]";
for (char ch : s.toCharArray()) {
if (openBrackets.indexOf(ch) != -1) {
stack[++i] = ch;
} else {
if (i >= 0 && openBrackets.indexOf(stack[i]) == closeBrackets.indexOf(ch)) {
i--;
} else {
return false;
}
throw new IllegalArgumentException("Unexpected character: " + c);
}
}
return i == -1;

return stack.isEmpty();
}
}
26 changes: 7 additions & 19 deletions src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
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Original file line number Diff line number Diff line change
@@ -1,27 +1,15 @@
package com.thealgorithms.strings;

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.assertEquals;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;

public class ValidParenthesesTest {

@Test
void testOne() {
assertTrue(ValidParentheses.isValid("()"));
assertTrue(ValidParentheses.isValidParentheses("()"));
}

@Test
void testTwo() {
assertTrue(ValidParentheses.isValid("()[]{}"));
assertTrue(ValidParentheses.isValidParentheses("()[]{}"));
}

@Test
void testThree() {
assertFalse(ValidParentheses.isValid("(]"));
assertFalse(ValidParentheses.isValidParentheses("(]"));
@ParameterizedTest(name = "Input: \"{0}\" → Expected: {1}")
@CsvSource({"'()', true", "'()[]{}', true", "'(]', false", "'{[]}', true", "'([{}])', true", "'([)]', false", "'', true", "'(', false", "')', false"})
void testIsValid(String input, boolean expected) {
assertEquals(expected, ValidParentheses.isValid(input));
}
}
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