剑指offer_包含min函数的栈

设计一个支持push，pop，top等操作并且可以在O(1)时间内检索出最小元素的堆栈。

• push(x)–将元素x插入栈中
• pop()–移除栈顶元素
• top()–得到栈顶元素
• getMin()–得到栈中最小元素

code

/**
 * initialize your data structure here.
 */
var MinStack = function() {
    this.x_stack = [];
    this.min_stack = [Infinity];
};

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

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    this.x_stack.pop()
    this.min_stack.pop()
};

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

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

/** 
 * Your MinStack object will be instantiated and called as such:
 * var obj = Object.create(MinStack).createNew()
 * obj.push(x)
 * obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.getMin()
 */