Add ValidParentheses (#3689)

DIRECTORY.md

@@ -477,6 +477,7 @@
             * [ReverseStringRecursive](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/ReverseStringRecursive.java)
             * [Rotation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Rotation.java)
             * [Upper](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Upper.java)
+            * [ValidParentheses](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/ValidParentheses.java)
             * [WordLadder](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/WordLadder.java)
             * zigZagPattern
               * [zigZagPattern](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/zigZagPattern/zigZagPattern.java)
@@ -648,6 +649,7 @@
             * [ReverseStringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/ReverseStringTest.java)
             * [RotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/RotationTest.java)
             * [UpperTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/UpperTest.java)
+            * [ValidParenthesesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java)
             * [WordLadderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/WordLadderTest.java)
             * zigZagPattern
               * [zigZagPatternTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/zigZagPattern/zigZagPatternTest.java)

src/main/java/com/thealgorithms/strings/ValidParentheses.java

@@ -0,0 +1,33 @@
+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.
+
+
+public class ValidParentheses {
+	public static boolean isValid(String s) {
+		char[] stack = new char[s.length()];
+		int head = 0;
+		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] != '[') return false;
+					break;
+			}
+		}
+		return head == 0;
+	}
+}

src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java

@@ -0,0 +1,24 @@
+package com.thealgorithms.strings;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ValidParenthesesTest {
+	
+    @Test
+    void testOne() {
+        assertEquals(true, ValidParentheses.isValid("()"));
+    }
+  
+    @Test
+    void testTwo() {
+        assertEquals(true, ValidParentheses.isValid("()[]{}"));
+    }
+  
+  
+    @Test
+    void testThree() {
+        assertEquals(false, ValidParentheses.isValid("(]"));
+    }
+	
+}