题目地址：https://leetcode.com/problems/design-circular-deque/description/
题目描述：
Design your implementation of the circular double-ended queue (deque). Your implementation should support following operations:
- MyCircularDeque(k): Constructor, set the size of the deque to be k.
- insertFront(): Adds an item at the front of Deque. Return true if the operation is successful.
- insertLast(): Adds an item at the rear of Deque. Return true if the operation is successful.
- deleteFront(): Deletes an item from the front of Deque. Return true if the operation is successful.
- deleteLast(): Deletes an item from the rear of Deque. Return true if the operation is successful.
- getFront(): Gets the front item from the Deque. If the deque is empty, return -1.
- getRear(): Gets the last item from Deque. If the deque is empty, return -1.
- isEmpty(): Checks whether Deque is empty or not.
- isFull(): Checks whether Deque is full or not.
Example:
MyCircularDeque circularDeque = new MycircularDeque(3); // set the size to be 3
circularDeque.insertLast(1); // return true
circularDeque.insertLast(2); // return true
circularDeque.insertFront(3); // return true
circularDeque.insertFront(4); // return false, the queue is full
circularDeque.getRear(); // return 32
circularDeque.isFull(); // return true
circularDeque.deleteLast(); // return true
circularDeque.insertFront(4); // return true
circularDeque.getFront(); // return 4
Note:
- All values will be in the range of [1, 1000].
- The number of operations will be in the range of [1, 1000].
- Please do not use the built-in Deque library.
题目大意
实现一个双向环形链表。
解题方法
使用列表
和622. Design Circular Queueopen in new window很类似了，622题要求的是单向的环形链表，这个题要求是双向的。
做法同样是采用和622题目类似的“作弊”做法，用一个list实现类似的环形列表。因为是双向链表，所以可以从头尾插入元素，对应了list的insert和append方法。
特别注意的是，插入元素，无论是在头尾插入，要移动的指针都是rear。
我这个题的做法比622更加成熟一点，622是通过头部指针来实现的，这个题里面是直接操作的头部元素导致后面的元素跟着变化，头部指针没有用到。。
这么一说可以把头部指针删除了23333.
在这么一说发现rear一直指向的是list的结尾，所以也可以删除了23333.
没删除头部指针的代码如下：
class MyCircularDeque(object):
def __init__(self, k):
"""
Initialize your data structure here. Set the size of the deque to be k.
:type k: int
"""
self.queue = []
self.size = k
self.front = 0
self.rear = 0
def insertFront(self, value):
"""
Adds an item at the front of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.insert(0, value)
self.rear += 1
return True
else:
return False
def insertLast(self, value):
"""
Adds an item at the rear of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.append(value)
self.rear += 1
return True
else:
return False
def deleteFront(self):
"""
Deletes an item from the front of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop(0)
self.rear -= 1
return True
else:
return False
def deleteLast(self):
"""
Deletes an item from the rear of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop()
self.rear -= 1
return True
else:
return False
def getFront(self):
"""
Get the front item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[self.front]
def getRear(self):
"""
Get the last item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[self.rear -1]
def isEmpty(self):
"""
Checks whether the circular deque is empty or not.
:rtype: bool
"""
return self.front == self.rear
def isFull(self):
"""
Checks whether the circular deque is full or not.
:rtype: bool
"""
return self.rear - self.front == self.size
# Your MyCircularDeque object will be instantiated and called as such:
# obj = MyCircularDeque(k)
# param_1 = obj.insertFront(value)
# param_2 = obj.insertLast(value)
# param_3 = obj.deleteFront()
# param_4 = obj.deleteLast()
# param_5 = obj.getFront()
# param_6 = obj.getRear()
# param_7 = obj.isEmpty()
# param_8 = obj.isFull()
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其实可以删除头指针，因为头指针一直指向0.
删除头部指针的代码如下：
class MyCircularDeque(object):
def __init__(self, k):
"""
Initialize your data structure here. Set the size of the deque to be k.
:type k: int
"""
self.queue = []
self.size = k
self.rear = 0
def insertFront(self, value):
"""
Adds an item at the front of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.insert(0, value)
self.rear += 1
return True
else:
return False
def insertLast(self, value):
"""
Adds an item at the rear of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.append(value)
self.rear += 1
return True
else:
return False
def deleteFront(self):
"""
Deletes an item from the front of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop(0)
self.rear -= 1
return True
else:
return False
def deleteLast(self):
"""
Deletes an item from the rear of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop()
self.rear -= 1
return True
else:
return False
def getFront(self):
"""
Get the front item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[0]
def getRear(self):
"""
Get the last item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[self.rear -1]
def isEmpty(self):
"""
Checks whether the circular deque is empty or not.
:rtype: bool
"""
return 0 == self.rear
def isFull(self):
"""
Checks whether the circular deque is full or not.
:rtype: bool
"""
return self.rear == self.size
# Your MyCircularDeque object will be instantiated and called as such:
# obj = MyCircularDeque(k)
# param_1 = obj.insertFront(value)
# param_2 = obj.insertLast(value)
# param_3 = obj.deleteFront()
# param_4 = obj.deleteLast()
# param_5 = obj.getFront()
# param_6 = obj.getRear()
# param_7 = obj.isEmpty()
# param_8 = obj.isFull()
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rear 始终等于 len(self.queue)，所以完全可以删除。
删除front和rear指针的代码如下：
class MyCircularDeque(object):
def __init__(self, k):
"""
Initialize your data structure here. Set the size of the deque to be k.
:type k: int
"""
self.queue = []
self.size = k
def insertFront(self, value):
"""
Adds an item at the front of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.insert(0, value)
return True
else:
return False
def insertLast(self, value):
"""
Adds an item at the rear of Deque. Return true if the operation is successful.
:type value: int
:rtype: bool
"""
if not self.isFull():
self.queue.append(value)
return True
else:
return False
def deleteFront(self):
"""
Deletes an item from the front of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop(0)
return True
else:
return False
def deleteLast(self):
"""
Deletes an item from the rear of Deque. Return true if the operation is successful.
:rtype: bool
"""
if not self.isEmpty():
self.queue.pop()
return True
else:
return False
def getFront(self):
"""
Get the front item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[0]
def getRear(self):
"""
Get the last item from the deque.
:rtype: int
"""
if self.isEmpty():
return -1
else:
return self.queue[-1]
def isEmpty(self):
"""
Checks whether the circular deque is empty or not.
:rtype: bool
"""
return 0 == len(self.queue)
def isFull(self):
"""
Checks whether the circular deque is full or not.
:rtype: bool
"""
return self.size == len(self.queue)
# Your MyCircularDeque object will be instantiated and called as such:
# obj = MyCircularDeque(k)
# param_1 = obj.insertFront(value)
# param_2 = obj.insertLast(value)
# param_3 = obj.deleteFront()
# param_4 = obj.deleteLast()
# param_5 = obj.getFront()
# param_6 = obj.getRear()
# param_7 = obj.isEmpty()
# param_8 = obj.isFull()
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双向链表
上面的解法直接使用了内置数据结构list，在头部插入的效率比较慢，时间复杂度是O(N)！所以我使用了双向链表模拟deque.
维护双向链表的方式和STL的list一样。对啊，可以直接用List。。方法就不仔细讲了。
struct Node {
Node* prev;
Node* next;
int val;
Node(int v) : val(v) {};
};
struct List {
Node* dummy;
int size;
List() : size(0) {
dummy = new Node(0);
dummy->next = dummy;
dummy->prev = dummy;
};
};
class MyCircularDeque {
public:
/** Initialize your data structure here. Set the size of the deque to be k. */
MyCircularDeque(int k) {
maxSize = k;
}
/** Adds an item at the front of Deque. Return true if the operation is successful. */
bool insertFront(int value) {
if (list.size == maxSize)
return false;
Node* cur = new Node(value);
Node* prev = list.dummy->prev;
list.dummy->prev = cur;
cur->prev = prev;
prev->next = cur;
cur->next = list.dummy;
++list.size;
return true;
}
/** Adds an item at the rear of Deque. Return true if the operation is successful. */
bool insertLast(int value) {
if (list.size == maxSize)
return false;
Node* cur = new Node(value);
Node* next = list.dummy->next;
list.dummy->next = cur;
cur->next = next;
next->prev = cur;
cur->prev = list.dummy;
++list.size;
return true;
}
/** Deletes an item from the front of Deque. Return true if the operation is successful. */
bool deleteFront() {
if (list.size == 0) return false;
Node* prev = list.dummy->prev;
Node* pprev = prev->prev;
list.dummy->prev = pprev;
pprev->next = list.dummy;
--list.size;
return true;
}
/** Deletes an item from the rear of Deque. Return true if the operation is successful. */
bool deleteLast() {
if (list.size == 0) return false;
Node* next = list.dummy->next;
Node* nnext = next->next;
list.dummy->next = nnext;
nnext->prev = list.dummy;
--list.size;
return true;
}
/** Get the front item from the deque. */
int getFront() {
if (list.size == 0) return -1;
return list.dummy->prev->val;
}
/** Get the last item from the deque. */
int getRear() {
if (list.size == 0) return -1;
return list.dummy->next->val;
}
/** Checks whether the circular deque is empty or not. */
bool isEmpty() {
return list.size == 0;
}
/** Checks whether the circular deque is full or not. */
bool isFull() {
return list.size == maxSize;
}
private:
List list;
int maxSize;
};
/**
* Your MyCircularDeque object will be instantiated and called as such:
* MyCircularDeque obj = new MyCircularDeque(k);
* bool param_1 = obj.insertFront(value);
* bool param_2 = obj.insertLast(value);
* bool param_3 = obj.deleteFront();
* bool param_4 = obj.deleteLast();
* int param_5 = obj.getFront();
* int param_6 = obj.getRear();
* bool param_7 = obj.isEmpty();
* bool param_8 = obj.isFull();
*/
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