LeetCode-155. Min Stack

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问题描述

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

Implement the MinStack class:

  • MinStack() initializes the stack object.
  • void push(int val) pushes the element val onto the stack.
  • void pop() removes the element on the top of the stack.
  • int top() gets the top element of the stack.
  • int getMin() retrieves the minimum element in the stack.

Example :

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Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output
[null,null,null,null,-3,null,0,-2]

Explanation
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top();    // return 0
minStack.getMin(); // return -2

解答

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/*
 * @Description: 155. Min Stack
 * @Author: libk
 * @Github: https://github.com/libk
 */
/** 
 * Your MinStack object will be instantiated and called as such:
 * var obj = new MinStack()
 * obj.push(val)
 * obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.getMin()
 */

const MinStack = function () {
  this.stack = []
  this.min = [Infinity]
}

/**
 * @param {number} val
 * @return {void}
 */
MinStack.prototype.push = function (val) {
  this.stack.push(val)
  this.min.push(Math.min(val, this.min[this.min.length - 1]))
}

/**
 * @return {void}
 */
MinStack.prototype.pop = function () {
  this.stack.pop()
  this.min.pop()
}

/**
 * @return {number}
 */
MinStack.prototype.top = function () {
  return this.stack[this.stack.length - 1]
}

/**
 * @return {number}
 */
MinStack.prototype.getMin = function () {
  return this.min[this.min.length - 1]
}