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.
解法：
/**
* initialize your data structure here.
*/
var MinStack = function() {
this.stack=[];
};
/**
* @param {number} x
* @return {void}
*/
MinStack.prototype.push = function(x) {
var min=x;
if(this.stack.length>0){
min=Math.min(this.stack[this.stack.length-1].min,x);
}
this.stack.push({val:x,min:min})
};
/**
* @return {void}
*/
MinStack.prototype.pop = function() {
if(this.stack.length>0){
return this.stack.pop().val;
}
};
/**
* @return {number}
*/
MinStack.prototype.top = function() {
return this.stack[this.stack.length-1].val;
};
/**
* @return {number}
*/
MinStack.prototype.getMin = function() {
return this.stack[this.stack.length-1].min;
};
/**
* 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()
*/