面试题 21: 包含min函数的栈

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一. 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的时间复杂度都是O(1).

代码请到我的代码库中下载 Point2Offer

二. 代码

package week_5;import java.util.Stack;/**难度系数:*** * 剑指offer: 包含min函数的栈 * 方法: 建一个辅助栈,存最小值 * 测试用例: * @author dingding * Date:2017-7-11 21:40 * Declaration: All Rights Reserved! */public class No21 {    public static void main(String[] args) {        test1();        test2();        test3();        test4();    }    //定义新栈    public static class CStack{        private Stack<Integer> stack_data = new Stack<>();        private Stack<Integer> stack_min = new Stack<>();        private void push(Integer number){            stack_data.add(number);            if (stack_min.isEmpty() || number<stack_min.peek()) {                stack_min.add(number);            }else {                stack_min.add(stack_min.peek());            }        }        private int pop(){            if (stack_data.isEmpty() && stack_min.isEmpty()) {                throw new RuntimeException("The stack is already empty");            }            stack_min.pop();            return stack_data.pop();        }        private int min(){            if (!stack_data.isEmpty() && !stack_min.isEmpty()) {                return stack_min.peek();            }else {                throw new RuntimeException("No more element.");            }        }    }    /*===================测试用例=============*/    //入栈比前一个大的数    private static void test4() {        CStack cStack = new CStack();        cStack.push(3);        cStack.push(4);        int result = cStack.min();        System.out.println(result);        System.out.println();    }    //入栈比前一个小的数    private static void test3() {        CStack cStack = new CStack();        cStack.push(3);        cStack.push(4);        cStack.push(2);        int result = cStack.min();        System.out.println(result);        System.out.println();           }    //弹出栈不是最小的数    private static void test2() {        CStack cStack = new CStack();        cStack.push(1);        cStack.push(3);        cStack.push(4);        cStack.pop();        int result = cStack.min();        System.out.println(result);        System.out.println();               }    //弹出栈是最小的数    private static void test1() {        CStack cStack = new CStack();        cStack.push(3);        cStack.push(4);        cStack.push(2);        cStack.push(1);        cStack.pop();        int result = cStack.min();        System.out.println(result);        System.out.println();           }}

有不妥当之处,麻烦告知:D

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