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gistfile1.txt

             5               
         /       \             
      3            8
    /   \       /     \      
  2      4    6       9     
                \
                  7

def nextLargest(node):
    if it does not have a right child node:
        recursively go to parent until reach a larger node
        parent = node.parent
        while True and node.parent:
            if parent.left == node:
                return parent
            else:
                node = node.parent
    if it has right child node:
        it should go to the right child node
        while right_node.left:
           right_node = right_node.left
        return right_node
       
 

class LinkedNode(object):
    

class LRUCache(object):        
    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = {}
        self.key_node = {}
        self.head = LinkedNode(None)
        self.tail = LinkedNode(None)
        
        
        
    def set(self, key, value):
        if len(self.cache) >= self.capacity:
            last_recent = self.head.key
            del self.cache[last_recent]
            del self.key_node[last_recent]
            temp = self.head.next
            self.head.next = None
            temp.pre = None
        
        self.cache[key] = value
        node = LinkedNone(key)
        self.tail.next = node
        node.pre = self.tail
        self.tail = node
        self.key_node[key] = node