package com.peter.java.dsa.interfaces;
/**
 * 栈操作定义
 * 
 * @author Peter Pan
 */
public interface Stack<T> {
 /* 判空 */
 Boolean isEmpty();
 /* 清空栈 */
 void clear();
 /* 弹栈 */
 T pop();
 /* 入栈 */
 Boolean push(T data);
 /* 栈的长度 */
 int length();
 /* 查看栈顶的元素，但不移除它 */
 T peek();
 /* 返回对象在栈中的位置 */
 int search(T data);
}

package com.peter.java.dsa.common;
import com.peter.java.dsa.interfaces.Stack;
/**
 * 线性栈
 * 
 * @author Peter Pan
 */
public class LinearStack<T> implements Stack<T> {
 @SuppressWarnings("unchecked")
  private T[] t = (T[]) new Object[16];
 private int size = 0;
 @Override
  public Boolean isEmpty() {
  // TODO Auto-generated method stub
  return size == 0;
 }
 @Override
  public void clear() {
  // TODO Auto-generated method stub
  for (int i = 0; i < t.length; i++) {
   t[i] = null;
  }
  size = 0;
 }
 @Override
  public T pop() {
  // TODO Auto-generated method stub
  if (size == 0) {
   return null;
  }
  T tmp = t[size - 1];
  t[size - 1] = null;
  size--;
  return tmp;
 }
 @Override
  public Boolean push(T data) {
  // TODO Auto-generated method stub
  if (size >= t.length) {
   resize();
  }
  t[size++] = data;
  return true;
 }
 @Override
  public int length() {
  // TODO Auto-generated method stub
  return size;
 }
 @Override
  public T peek() {
  // TODO Auto-generated method stub
  if (size == 0) {
   return null;
  } else {
   return t[size - 1];
  }
 }
 /* return index of data, return -1 if no data */
 @Override
  public int search(T data) {
  // TODO Auto-generated method stub
  int index = -1;
  for (int i = 0; i < t.length; i++) {
   if (t[i].equals(data)) {
    index = i;
    break;
   }
  }
  return index;
 }
 @SuppressWarnings("unchecked")
  private void resize() {
  T[] tmp = (T[]) new Object[t.length * 2];
  for (int i = 0; i < t.length; i++) {
   tmp[i] = t[i];
   t[i] = null;
  }
  t = tmp;
  tmp = null;
 }
 /* from the left to the right is from the top to the bottom of the stack */
 @Override
  public String toString() {
  // TODO Auto-generated method stub
  StringBuffer buffer = new StringBuffer();
  buffer.append("Linear Stack Content:[");
  for (int i = t.length - 1; i > -1; i--) {
   buffer.append(t[i].toString() + ",");
  }
  buffer.append("]");
  buffer.replace(buffer.lastIndexOf(","), buffer.lastIndexOf(",") + 1, "");
  return buffer.toString();
 }
}

package com.peter.java.dsa.common;
import com.peter.java.dsa.interfaces.Stack;
public class LinkedStack<T> implements Stack<T> {
 private Node top;
 private int size;
 @Override
  public Boolean isEmpty() {
  // TODO Auto-generated method stub
  return size == 0;
 }
 @Override
  public void clear() {
  // TODO Auto-generated method stub
  top = null;
  size = 0;
 }
 @Override
  public T pop() {
  // TODO Auto-generated method stub
  T topValue = null;
  if (top != null) {
   topValue = top.data;
   Node oldTop = top;
   top = top.prev;
   oldTop.prev = null;
   size--;
  }
  return topValue;
 }
 @Override
  public Boolean push(T data) {
  // TODO Auto-generated method stub
  Node oldTop = top;
  top = new Node(data);
  top.prev = oldTop;
  size++;
  return true;
 }
 @Override
  public int length() {
  // TODO Auto-generated method stub
  return size;
 }
 @Override
  public T peek() {
  // TODO Auto-generated method stub
  T topValue = null;
  if (top != null) {
   topValue = top.data;
  }
  return topValue;
 }
 @Override
  public int search(T data) {
  // TODO Auto-generated method stub
  int index = -1;
  Node tmp = top;
  for (int i = size - 1; i > -1; i--) {
   if (tmp.data.equals(data)) {
    index = i;
    break;
   } else {
    tmp = tmp.prev;
   }
  }
  tmp = null;
  return index;
 }
 @Override
  public String toString() {
  // TODO Auto-generated method stub
  StringBuffer buffer = new StringBuffer();
  buffer.append("Linked Stack Content:[");
  Node tmp = top;
  for (int i = 0; i < size - 1; i++) {
   buffer.append(tmp.toString() + ",");
   tmp = tmp.prev;
  }
  tmp = null;
  buffer.append("]");
  buffer.replace(buffer.lastIndexOf(","), buffer.lastIndexOf(",") + 1, "");
  return super.toString();
 }
 private class Node {
  T data;
  Node prev;
  public Node(T data) {
   // TODO Auto-generated constructor stub
   this.data = data;
  }
 }
}