Create JavaStack.java

Author: AD9000

Data Structures/JavaStack.java

@@ -0,0 +1,54 @@
+// Author: Atharv Damle
+// Use a stack to see if paranthesis in a String is balanced.
+// Full Question: https://www.hackerrank.com/challenges/java-stack/problem
+
+// Logic: Add the opening brackets in a stack. Remove the top bracket if its match is found.
+// If the stack is empty at the end of the string, it is balanced (as all brackets are now in pairs), else it is not.
+
+import java.util.*;
+class JavaStack
+{
+	public static void main(String []args)
+	{
+		Scanner sc = new Scanner(System.in);
+		
+		while (sc.hasNext()) {
+			String input=sc.next();
+            int l = input.length();
+            
+            // Deque is the recommended Java implementation of stack. It will take in Character type data
+            Deque<Character> s = new ArrayDeque<>();
+            
+            for (int i = 0; i < l; i++)
+            {
+              char ch = input.charAt(i);
+              
+              // peek() function returns the next element that can be removed from the stack
+              // Pairs of brackets have a maximum difference of 2. (According to the ASCII Table)
+              if (!s.isEmpty() && ((s.peek() == ch - 1) || (s.peek() == ch - 2)))
+              {
+                  // Remove element from top of stack
+                  s.removeFirst();
+              }
+              else
+              {
+                  // Add element to the top of stack.
+                  s.addFirst(ch);
+              }
+            }
+            
+            // If the stack is not empty...
+            if (!s.isEmpty())
+            {
+              System.out.println(false);
+            }
+            else
+            {
+              System.out.println(true);
+            }
+		}
+	}
+}
+
+
+