LeetCode之Min Stack

1.原文问题描述:

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
getMin() -- Retrieve the minimum element in the stack.

2.问题翻译

设计一个栈,使它能够同时支持 push, pop, top方法并且能够同时检索最小值
push(x) -- 把元素X放到栈中
pop() --将栈顶元素移除
top() --获取栈顶元素
getMin() --检索出栈中最小的值

3.解决思路

  a:最简单直接的就是通过Java自己提供的栈,然后因为栈提供了出栈(pop())进栈(push())还有栈顶元素(peek())的方法,我们需要做的就是宁外设置一个变量或者使用一个其他的栈来保持最小的元素,在进栈出栈的时候来更新这个值,从而就可以获取到了最小值了

  b:不使用Java提供的内置栈的实现方式,这个需要我们来模仿栈的实现过程

4.实现方式(b)

节点的定义(Node.java)

package minStack;

/**
 * 栈中的节点定义(保存节点元素的同时需要保存栈中最小的元素的值)
 * @author wudy
 *
 */
class Node {

    int value;//当前元素的值
    int minValue;//用来保存栈中最小的元素(只需要在站定元素中设置这个属性就行了)
    Node next;//指向下一节点,模仿栈的实现

    /**
     * 构造函数,实例化栈的节点
     * @param value
     */
    public Node(int value) {
        this.value = value;
    }
}

 最小值栈的实现(MinStack.java)

package minStack;

class MinStack {

    Node top = null;

    /**
     * 入栈,在入栈的同时需要检查更新元素的最小值
     * @param x
     */
    public void push(int x) {
        if (top == null) {
            top = new Node(x);
            top.minValue = x;
        } else {
            Node temp = new Node(x);
            temp.next = top;
            top = temp;
            top.minValue = Math.min(top.next.minValue, x);
        }
    }

    /**
     * 出栈,只需要将当前元素节点的指针指向下一个元素即可
     */
    public void pop() {
        top = top.next;
        return;
    }

    /**
     * 获取栈顶元素(不为空则返回具体的值)
     * @return
     */
    public int top() {
        return top == null ? 0 : top.value;
    }

    /**
     * 从栈顶元素中拿到最小值
     * @return
     */
    public int getMin() {
        return top == null ? 0 : top.minValue;
    }
}

 测试类(MinStackTest.java)

package minStack;

public class MinStackTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		MinStack minStack = new MinStack();

		for(int index = 0;index < 10;index++){
			minStack.push(index);
		}

		System.out.println("栈顶元素:"+minStack.top());
		System.out.println("最小元素:"+minStack.getMin());
		System.out.println("栈顶元素出栈");

		minStack.pop();

		System.out.println("栈顶元素:"+minStack.top());
		System.out.println("最小元素:"+minStack.getMin());
	}

}

 5.主要考察了数据结构中栈的实现和定义,比较简单

时间: 2024-10-11 01:44:32

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