面試題 21: 包含min函數的棧

一. 題目

定義棧的數據結構,請在該類型中實現一個能夠得到棧的最小元素的min 函數.在該棧中,調用min,push 及pop的時間複雜度都是O(1).

代碼請到我的代碼庫中下載 Point2Offer

二. 代碼

package week_5;

import java.util.Stack;

/**難度係數:***
 * 劍指offer: 包含min函數的棧
 * 方法: 建一個輔助棧,存最小值
 * 測試用例:
 * @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();
    }

    //定義新棧
    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.");
            }
        }

    }
    /*===================測試用例=============*/
    //入棧比前一個大的數
    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();

    }
    //入棧比前一個小的數
    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();       
    }

    //彈出棧不是最小的數
    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();           
    }
    //彈出棧是最小的數
    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();       
    }

}

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有不妥當之處,麻煩告知:D