Moved StackPostfixNotation.java from the Others section to the Stack section (#4372)

* Moved StackPostfixNotation.java from the Others section to the Stack section

* Put all stack related algo in a separate stack directory in the algorithms directory. The stack directory under data-structures now only contains various implementations of the stack data structure.

* formatted files

src/main/java/com/thealgorithms/stacks/DuplicateBrackets.java

@@ -0,0 +1,43 @@
+package com.thealgorithms.stacks;
+
+//  1. You are given a string exp representing an expression.
+// 2. Assume that the expression is balanced  i.e. the opening and closing brackets match with each
+// other.
+// 3. But, some of the pair of brackets maybe extra/needless.
+// 4. You are required to print true if you detect extra brackets and false otherwise.
+// e.g.'
+// ((a + b) + (c + d)) -> false
+// (a + b) + ((c + d)) -> true
+import java.util.*;
+
+public class DuplicateBrackets {
+
+    public static boolean check(String str) {
+        Stack<Character> st = new Stack<>();
+
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            if (ch == ')') {
+                if (st.peek() == '(') {
+                    return true;
+                } else {
+                    while (st.size() > 0 && st.peek() != '(') {
+                        st.pop();
+                    }
+                    st.pop();
+                }
+            } else {
+                st.push(ch);
+            }
+            // System.out.println(st);
+        }
+        return false;
+    }
+
+    public static void main(String[] args) throws Exception {
+        Scanner sc = new Scanner(System.in);
+        String str = sc.nextLine();
+        System.out.println(check(str));
+        sc.close();
+    }
+}