155. Min Stack（js）

155. Min Stack

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.

Example:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

题意：设计一个数据结构，有push（入栈）,pop（出栈）,top（查看栈顶元素）,getMin（查看栈最小元素）等方法
代码如下：

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

/** 
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
    this.data.push(x);
};

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

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

/**
 * @return {number}
 */
MinStack.prototype.getMin = function() {
    return Math.min(...this.data);
};

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