MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> 返回 -3.
minStack.pop();
minStack.top(); --> 返回 0.
minStack.getMin(); --> 返回 -2.
const minStack = function(){
this.stack = []
// 辅助栈，换更少的时间复杂度
this.stack2 = []
}
minStack.prototype.push = function(x){
this.stack.push(x)
// 如果入栈比辅助栈的栈顶元素小或者相等，则入辅助栈
if(this.stack2.length ==0 || this.stack2[this.stack.length-1>=x]){
this.stack2.push(x)
}
}
minStack.prototype.pop = function(){
// 如果主栈出栈的值小于等于辅助栈栈顶元素，辅助栈也要出栈，确保getMin一直是栈中的最小值
if(this.stack.pop() == this.stack2[this.stack2.length - 1]){
return this.stack2.pop()
}
}
minStack.prototype.top = function(){
return this.stack[this.stack.length-1]
}
minstack.prototype.getMin = function(){
return this.stack2[this.stack2.length -1 ]
}