02. 栈的最小值

https://leetcode-cn.com/problems/min-stack-lcci/

Java

/*
 * @Author: Goog Tech
 * @Date: 2020-09-01 21:57:05
 * @LastEditTime: 2020-09-01 22:07:53
 * @Description: https://leetcode-cn.com/problems/min-stack/
 * @FilePath: \leetcode-googtech\面试题03\#02. 栈的最小值\Solution.java
 * @WebSite: https://algorithm.show/
 */

class MinStack {

    // 声明两个辅助栈,其中 stack 用于存储元素,而 minStack 仅用于存储 stack 中的最小元素
    private Stack<Integer> stack;
    private Stack<Integer> minStack;

    /** initialize your data structure here. */
    public MinStack() {
        // 初始化辅助栈
        stack = new Stack<>();
        minStack = new Stack<>();
    }

    public void push(int x) {
        // 将元素压入 stack 栈中
        stack.push(x);
        // 若当前 minStack 为空或其顶部元素小于或等于当前压入的元素 x,则将 x 压入 minStack 栈中
        if(minStack.isEmpty() || x <= minStack.peek()) {
            minStack.push(x);
        }
    }

    public void pop() {
        // 弹出 stack 栈的顶部元素,若其与 minStack 栈的顶部元素相同,则也弹出 minStack 栈的顶部元素
        // 进而可以保证 minStack 的栈顶元素始终是 stack 栈中的最小值
        if(stack.pop().equals(minStack.peek())) {
            minStack.pop();
        }
    }

    public int top() {
        // 获取 stack 栈的顶部元素
        return stack.peek();
    }

    public int getMin() {
        // 获取 minStack 栈的顶部元素,即所压入元素的最小值
        return minStack.peek();
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */

Python

'''
Author: Goog Tech
Date: 2020-09-01 21:57:09
LastEditTime: 2020-09-01 22:08:14
Description: https://leetcode-cn.com/problems/min-stack/
FilePath: \leetcode-googtech\面试题03\#02. 栈的最小值\Solution.py
WebSite: https://algorithm.show/
'''

class MinStack(object):

    def __init__(self):
        """
        initialize your data structure here.
        """
        # 初始化两个辅助栈,其中 stack 用于存储元素,而 minStack 仅用于存储 stack 中的最小元素
        self.stack = []
        self.minStack = []

    def push(self, x):
        """
        :type x: int
        :rtype: None
        """
        # 将元素压入 stack 栈中
        self.stack.append(x)
        # 若当前 minStack 为空或其顶部元素小于或等于当前压入的元素 x,则将 x 压入 minStack 栈中
        if not self.minStack or x <= self.minStack[-1]:
            self.minStack.append(x)

    def pop(self):
        """
        :rtype: None
        """
        # 弹出 stack 栈的顶部元素,若其与 minStack 栈的顶部元素相同,则也弹出 minStack 栈的顶部元素
        # 进而可以保证 minStack 的栈顶元素始终是 stack 栈中的最小值
        if self.stack.pop() == self.minStack[-1]:
            self.minStack.pop()

    def top(self):
        """
        :rtype: int
        """
        # 获取 stack 栈的顶部元素
        return self.stack[-1]

    def getMin(self):
        """
        :rtype: int
        """
        # 获取 minStack 栈的顶部元素,即所压入元素的最小值
        return self.minStack[-1]

# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()