Added Dynamic Stack

algorithms/Java/stacks/DynamicStack.java

@@ -0,0 +1,165 @@
+import java.io.*;
+
+/*
+1. You are given the code of our CustomStack class which mimics the java.util.Stack class.
+2. Here is the list of functions that are written in the class...
+    2.1. push -> Accepts new data if there is space available in the underlying array or
+     print "Stack overflow" otherwise
+     2.2. pop -> Removes and returns last data if available or print "Stack underflow"
+     otherwise and returns -1
+     2.3. top -> Return last data if available or print "Stack underflow" otherwise and
+      returns -1
+     2.4. size -> Returns the number of elements available in the stack
+     2.5. display -> Print the elements of stack in LIFO manner (space-separated)
+     ending with a line-break.
+3. Input and Output are managed for you.
+4. You are required to change the body of push function to accept the element even when the data array is completely full.
+ In that case, you are required to reallocate the data array (to twice it's size). You should not print "Stack overflow" ever.
+
+ Sample Input
+
+5
+push 10
+display
+push 20
+display
+push 30
+display
+push 40
+display
+push 50
+display
+push 60
+display
+top
+pop
+display
+top
+pop
+display
+top
+pop
+display
+top
+pop
+display
+top
+pop
+display
+top
+pop
+quit
+
+Sample Output
+
+10
+20 10
+30 20 10
+40 30 20 10
+50 40 30 20 10
+60 50 40 30 20 10
+60
+60
+50 40 30 20 10
+50
+50
+40 30 20 10
+40
+40
+30 20 10
+30
+30
+20 10
+20
+20
+10
+10
+10
+ */
+
+public class DynamicStack {
+    public static class CustomStack {
+        int[] data;
+        int tos;
+
+        public CustomStack(int cap) {
+            data = new int[cap];
+            tos = -1;
+        }
+
+        int size() {
+            return tos + 1;
+        }
+
+        void display() {
+            for (int i = tos; i >= 0; i--) {
+                System.out.print(data[i] + " ");
+            }
+            System.out.println();
+        }
+
+        // change the code of this function according to question
+        void push(int val) {
+            if (tos == data.length - 1) {
+                int[] oa = data;
+                data = new int[2*oa.length];
+                for (int i = 0; i < oa.length; i++) {
+                    data[i] = oa[i];
+                }
+
+            }
+                tos++;
+                data[tos] = val;
+
+        }
+
+        int pop() {
+            if (tos == -1) {
+                System.out.println("Stack underflow");
+                return -1;
+            } else {
+                int val = data[tos];
+                tos--;
+                return val;
+            }
+        }
+
+        int top() {
+            if (tos == -1) {
+                System.out.println("Stack underflow");
+                return -1;
+            } else {
+                return data[tos];
+            }
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        int n = Integer.parseInt(br.readLine());
+        CustomStack st = new CustomStack(n);
+
+        String str = br.readLine();
+        while (str.equals("quit") == false) {
+            if (str.startsWith("push")) {
+                int val = Integer.parseInt(str.split(" ")[1]);
+                st.push(val);
+            } else if (str.startsWith("pop")) {
+                int val = st.pop();
+                if (val != -1) {
+                    System.out.println(val);
+                }
+            } else if (str.startsWith("top")) {
+                int val = st.top();
+                if (val != -1) {
+                    System.out.println(val);
+                }
+            } else if (str.startsWith("size")) {
+                System.out.println(st.size());
+            } else if (str.startsWith("display")) {
+                st.display();
+            }
+            str = br.readLine();
+        }
+    }
+}