包含min函数的栈

题目：定义栈的数据结构，请在该类型中实现一个能够得到栈的最小元素的min函数。在该栈中，调用min,push及pop的时间复杂度是O（1）。思路：自定义栈内，另建一个栈，用于存储最小值的数组下标。即，入栈时，通过最小值索引栈，得到当前最小值下标，取数组对应值，如果比入栈的当前值大，则将当前值入栈下标，压入到索引栈中；出栈时，若当前出栈值的索引为索引栈的栈顶元素，则索引栈也进行栈顶元素出栈操作。算法代码：package disizhang;import java.util.Stack;/*** 自定义栈*/public class StackWithMin<E>{private int size = 16;//默认规模private int nextSize = 16;//超过范围，扩展操作private Object[] valArr;//存储数据结构private int index = -1;//栈顶下标private Stack<Integer> minStack;//存储最小值下标的栈/*** 构造器*/public StackWithMin(){valArr = new Object[size];minStack = new Stack<Integer>();}/*** 入栈* @param value*/public void push(E value){//不能为空if (null == value){throw new NullPointerException("Pushed value can not be null!");}//入参必须为可比较的if (!(value instanceof Comparable)){throw new UnsupportedOperationException("The value must be Comparable!");}//栈满了，重构栈if (index >= size){resetStack();}//入栈valArr[++index] = value;//最小值的索引入栈checkMinObj(value);}/*** 最小索引入栈思想* @param value*/@SuppressWarnings("unchecked")private void checkMinObj(E value){//第一个参数，直接为最小参数if (index == 0){minStack.push(index);return;}//入参的值Comparable valueComp = (Comparable) value;//当前最小值Comparable valueMinComp = (Comparable) valArr[minStack.peek()];//新入栈的值小于当前最小值，则当前索引入栈if (valueComp.compareTo(valueMinComp) < 0){minStack.push(index);}}/*** 出栈*/@SuppressWarnings("unchecked")public E pop(){//栈为空，报错if (index < 0){throw new NullPointerException("The statck is empty!");}//若是最小值出栈(比较下标判断)，需要将其索引出栈if (index == minStack.peek()){minStack.pop();}//出栈return (E) valArr[index--];}/*** 最小值*/@SuppressWarnings("unchecked")public E getMin(){//return (E) minArr[index];//笨办法//若栈空，则报错空指针if (index < 0){throw new NullPointerException("The statck is empty,no minValue returned!");}return (E) valArr[minStack.peek()];}/*** 重构栈*/private void resetStack(){size += nextSize;Object[] newArr = new Object[size];System.arraycopy(valArr, 0, newArr, 0, size - nextSize);valArr = newArr;}//测试public static void main(String[] args){//栈初始化//也可以直接使用Integer等实现了Comparable接口的封装类StackWithMin<MyValue> stack = new StackWithMin<MyValue>();//初始化几个值MyValue v1 = new MyValue(1);MyValue v2 = new MyValue(2);MyValue v3 = new MyValue(3);MyValue v4 = new MyValue(4);MyValue v5 = new MyValue(5);//入栈stack.push(v5);stack.push(v4);stack.push(v3);stack.push(v2);stack.push(v1);stack.push(v4);stack.push(v1);//最小值System.out.println("min: " + stack.getMin());//出栈System.out.println("pop: " + stack.pop());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());//最小值System.out.println("min: " + stack.getMin());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());System.out.println("min: " + stack.getMin());System.out.println("pop: " + stack.pop());}}/*** 自定义数值类*/class MyValueimplements Comparable<MyValue>{private int value;public MyValue(int value){this.value = value;}public int getValue(){return value;}public int compareTo(MyValue obj){//不能与null比较if (null == obj){throw new NullPointerException("Can not compare to null!");}return this.value - obj.getValue();}@Overridepublic String toString(){return "" + value;}}

本篇博文参考：http://blog.csdn.net/oh_maxy/article/details/11533345