Add ValidParentheses (#3689)

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;
+	}
+}