Initialization of a doubly linked list destroys insert Delete

Initialize: The end node of the head node is assigned a null value.
Delete: Determine the condition of the chain table length to make a conditional delete release

Insert: 1, insert after a node

2, insert in front of a node

1) A, allocation node failure return-1

b, the list length is 0.

The tail of the head is linked to the new node, and the end of the head of the new node is set to empty.

The normal insertion of four steps also determines whether the next node of the inserted node is empty.

2) A, check that the node space is allocated successfully.

b linked list length 0 normal thinking.

Determine if the node in front of the insertion position is empty normal thinking

Initialization of a doubly linked list destroys insert Delete