LeetCode - 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.

实现一个stack，要求有push,pop,top功能，还要有一个返回stack最小值的函数（要在常量时间里返回这个值）。在这里我用一个LinkList来实现stack，具体看下面代码。对于最小值，在每次添加或者删除的时候记录即可，这样就能在常量时间获得stack的最小值。

class MinStack {
    
    private LinkedList<Integer> list;
    private int min;
 
    
    
    /** initialize your data structure here. */
    public MinStack() {
        this.list = new LinkedList<Integer>();
        this.min = Integer.MAX_VALUE;
    }
    
    public void push(int x) {
        this.list.addFirst(x);
        if(x < this.min){
            this.min = x;
        }
    }
    
    public void pop() {
        int top = this.list.pollFirst();
        
        if(top == this.min){
            this.min = Integer.MAX_VALUE;
            for(int i : this.list){
                if(i < this.min){
                    this.min = i;
                }
            }
        }
    }
    
    public int top() {
        return this.list.peekFirst();
    }
    
    public int getMin() {
        return this.min;
    }
}

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