Java实现数据结构的栈和队列
栈是一种先进后出的数据结构, 首先定义了栈需要实现的接口:
Java代码
public interface MyStack { /** * 判断栈是否为空 */ boolean isEmpty(); /** * 清空栈 */ void clear(); /** * 栈的长度 */ int length(); /** * 数据入栈 */ boolean push(T data); /** * 数据出栈 */ T pop(); } public interface MyStack { /** * 判断栈是否为空 */ boolean isEmpty(); /** * 清空栈 */ void clear(); /** * 栈的长度 */ int length(); /** * 数据入栈 */ boolean push(T data); /** * 数据出栈 */ T pop(); }栈的数组实现, 底层使用数组:
public class MyArrayStack implements MyStack { private Object[] objs = new Object[16]; private int size = 0; @Override public boolean isEmpty() { return size == 0; } @Override public void clear() { // 将数组中的数据置为null, 方便GC进行回收 for (int i = 0; i = objs.length) { resize(); } objs[size++] = data; return true; } /** * 数组扩容 */ private void resize() { Object[] temp = new Object[objs.length * 3 / 2 + 1]; for (int i = 0; i implements MyStack { private Object[] objs = new Object[16]; private int size = 0; @Override public boolean isEmpty() { return size == 0; } @Override public void clear() { // 将数组中的数据置为null, 方便GC进行回收 for (int i = 0; i = objs.length) { resize(); } objs[size++] = data; return true; } /** * 数组扩容 */ private void resize() { Object[] temp = new Object[objs.length * 3 / 2 + 1]; for (int i = 0; i implements MyStack { /** * 栈顶指针 */ private Node top; /** * 栈的长度 */ private int size; public MyLinkedStack() { top = null; size = 0; } @Override public boolean isEmpty() { return size == 0; } @Override public void clear() { top = null; size = 0; } @Override public int length() { return size; } @Override public boolean push(T data) { Node node = new Node(); node.data = data; node.pre = top; // 改变栈顶指针 top = node; size++; return true; } @Override public T pop() { if (top != null) { Node node = top; // 改变栈顶指针 top = top.pre; size--; return node.data; } return null; } /** * 将数据封装成结点 */ private final class Node { private Node pre; private T data; } } public class MyLinkedStack implements MyStack { /** * 栈顶指针 */ private Node top; /** * 栈的长度 */ private int size; public MyLinkedStack() { top = null; size = 0; } @Override public boolean isEmpty() { return size == 0; } @Override public void clear() { top = null; size = 0; } @Override public int length() { return size; } @Override public boolean push(T data) { Node node = new Node(); node.data = data; node.pre = top; // 改变栈顶指针 top = node; size++; return true; } @Override public T pop() { if (top != null) { Node node = top; // 改变栈顶指针 top = top.pre; size--; return node.data; } return null; } /** * 将数据封装成结点 */ private final class Node { private Node pre; private T data; } }两种实现的比较, 主要比较数据入栈和出栈的速度:
Java代码 @Test public void testSpeed() { MyStack stack = new MyArrayStack(); int num = 10000000; long start = System.currentTimeMillis(); for (int i = 0; i stack = new MyArrayStack(); int num = 10000000; long start = System.currentTimeMillis(); for (int i = 0; i myStack = new MyArrayStack(); Integer result = num; while (true) { // 将余数入栈 myStack.push(result % n); result = result / n; if (result == 0) { break; } } StringBuilder sb = new StringBuilder(); // 按出栈的顺序倒序排列即可 while ((result = myStack.pop()) != null) { sb.append(result); } return sb.toString(); } private String conversion(int num, int n) { MyStack myStack = new MyArrayStack(); Integer result = num; while (true) { // 将余数入栈 myStack.push(result % n); result = result / n; if (result == 0) { break; } } StringBuilder sb = new StringBuilder(); // 按出栈的顺序倒序排列即可 while ((result = myStack.pop()) != null) { sb.append(result); } return sb.toString(); }2. 检验符号是否匹配. '['和']', '('和')'成对出现时字符串合法. 例如"[][]()", "[[([]([])()[])]]"是合法的; "([(])", "[())"是不合法的.
遍历字符串的每一个char, 将char与栈顶元素比较. 如果char和栈顶元素配对, 则char不入栈, 否则将char入栈. 当遍历完成时栈为空说明字符串是合法的.
public boolean isMatch(String str) { MyStack myStack = new MyArrayStack(); char[] arr = str.toCharArray(); for (char c : arr) { Character temp = myStack.pop(); // 栈为空时只将c入栈 if (temp == null) { myStack.push(c); } // 配对时c不入栈 else if (temp == '[' && c == ']') { } // 配对时c不入栈 else if (temp == '(' && c == ')') { } // 不配对时c入栈 else { myStack.push(temp); myStack.push(c); } } return myStack.isEmpty(); } public boolean isMatch(String str) { MyStack myStack = new MyArrayStack(); char[] arr = str.toCharArray(); for (char c : arr) { Character temp = myStack.pop(); // 栈为空时只将c入栈 if (temp == null) { myStack.push(c); } // 配对时c不入栈 else if (temp == '[' && c == ']') { } // 配对时c不入栈 else if (temp == '(' && c == ')') { } // 不配对时c入栈 else { myStack.push(temp); myStack.push(c); } } return myStack.isEmpty(); }3. 行编辑: 输入行中字符'#'表示退格, '@'表示之前的输入全都无效.
使用栈保存输入的字符, 如果遇到'#'就将栈顶出栈, 如果遇到@就清空栈. 输入完成时将栈中所有字符出栈后反转就是输入的结果:
private String lineEdit(String input) { MyStack myStack = new MyArrayStack(); char[] arr = input.toCharArray(); for (char c : arr) { if (c == '#') { myStack.pop(); } else if (c == '@') { myStack.clear(); } else { myStack.push(c); } } StringBuilder sb = new StringBuilder(); Character temp = null; while ((temp = myStack.pop()) != null) { sb.append(temp); } // 反转字符串 sb.reverse(); return sb.toString(); } 转载出处：http://coolxing.iteye.com/blog/1468674