removed duplciated data-structures

DataStructures/Stacks/BalancedBrackets.java

@@ -0,0 +1,89 @@
+package data_structures.Stacks;
+
+import java.util.Scanner;
+import java.util.Stack;
+
+/**
+ *
+ * The nested brackets problem is a problem that determines if a sequence of
+ * brackets are properly nested. A sequence of brackets s is considered properly
+ * nested if any of the following conditions are true: - s is empty - s has the
+ * form (U) or [U] or {U} where U is a properly nested string - s has the form
+ * VW where V and W are properly nested strings For example, the string
+ * "()()[()]" is properly nested but "[(()]" is not. The function called
+ * is_balanced takes as input a string S which is a sequence of brackets and
+ * returns true if S is nested and false otherwise.
+ *
+ * @author akshay sharma
+ * @date: 2017-10-17
+ * @author <a href="https://github.com/khalil2535">khalil2535<a>
+ *
+ */
+class BalancedBrackets {
+
+    /**
+     *
+     * @param s
+     * @return
+     */
+    static boolean is_balanced(String s) {
+        Stack<Character> bracketsStack = new Stack<>();
+        char[] text = s.toCharArray();
+        for (char x : text) {
+            switch (x) {
+                case '{':
+                case '<':
+                case '(':
+                case '[':
+                    bracketsStack.push(x);
+                    break;
+                case '}':
+                    if (bracketsStack.peek() == '{') {
+                        bracketsStack.pop();
+                        break;
+                    } else {
+                        return false;
+                    }
+                case '>':
+                    if (bracketsStack.peek() == '<') {
+                        bracketsStack.pop();
+                        break;
+                    } else {
+                        return false;
+                    }
+                case ')':
+                    if (bracketsStack.peek() == '(') {
+                        bracketsStack.pop();
+                        break;
+                    } else {
+                        return false;
+                    }
+                case ']':
+                    if (bracketsStack.peek() == '[') {
+                        bracketsStack.pop();
+                        break;
+                    } else {
+                        return false;
+                    }
+            }
+        }
+        return bracketsStack.empty();
+    }
+
+    /**
+     *
+     * @param args
+     * @TODO remove main method and Test using JUnit or other methodology
+     */
+    public static void main(String args[]) {
+        try (Scanner in = new Scanner(System.in)) {
+            System.out.println("Enter sequence of brackets: ");
+            String s = in.nextLine();
+            if (is_balanced(s)) {
+                System.out.println(s + " is balanced");
+            } else {
+                System.out.println(s + " ain't balanced");
+            }
+        }
+    }
+}

DataStructures/Stacks/StackOfLinkedList.java

@@ -15,6 +15,7 @@ class StackOfLinkedList {
         stack.push(2);
         stack.push(3);
         stack.push(4);
+        stack.push(5);
 
         stack.printStack();
 
@@ -23,6 +24,8 @@ class StackOfLinkedList {
         stack.pop();
         stack.pop();
 
+        System.out.println("Top element of stack currently is: " + stack.peek());
+
     }
 
 }
@@ -75,12 +78,20 @@ class LinkedListStack {
         System.out.println("Popped element is: " + temp.data);
     }
 
+    public int peek() {
+      if (getSize() == 0) {
+        return -1;
+      }
+
+      return head.data;
+    }
+
     public void printStack() {
 
         Node temp = head;
         System.out.println("Stack is printed as below: ");
         while (temp != null) {
-            System.out.print(temp.data + " ");
+            System.out.println(temp.data + " ");
             temp = temp.next;
         }
         System.out.println();
@@ -94,5 +105,5 @@ class LinkedListStack {
     public int getSize() {
         return size;
     }
-    
+
 }

DataStructures/Stacks/Stacks.java

@@ -53,16 +53,18 @@ class Stack{
 	 * @return value popped off the Stack
 	 */
 	public int pop(){
-		if(isEmpty()){ //Checks for an empty stack
-			System.out.println("The stack is already empty");
-			return -1;
+		if(!isEmpty()){ //Checks for an empty stack
+			return stackArray[top--];
 		}
 
 		if(top < maxSize/4){
 			resize(maxSize/2);
+			return pop();// don't forget pop after resizing
+		}
+		else{
+			System.out.println("The stack is already empty");
+			return -1;
 		}
-        
-        return stackArray[top--];
 	}
 
 	/**