面试题 21: 包含min函数的栈

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();
}

}