数据结构和算法，双向链表的实现增删改查(kotlin版)

1.定义接口，我们需要实现的方法

interface LinkedListAction<E> {
    fun push(e: E)
    fun size(): Int
    fun getValue(index: Int): E?
    fun insert(index: Int,e: E)
    fun remove(index: Int)
}

2.定义节点，表示每个链表节点。

data class Node<E>(var next: Node<E>? = null, var prev: Node<E>? = null, var value: E)

3.push(e: E)，链表尾部新增一个节点

override fun push(e: E) {
        linkLast(e)
        len++
    }
private fun linkLast(e: E) {
        var l = last
        val newNode = Node(null, last, e)
        last = newNode
        if (head != null) {
            l?.next = newNode
        } else {
            head = newNode
        }
    }

4.size(): Int，返回链表的长度

override fun size(): Int {
        return len
    }

5.getValue(index: Int): E?，获取列表的value值

   override fun getValue(index: Int): E? {
        if (index < 0 || index >= len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        return node(index)?.value
    }
	//找到对应index下标的节点。
    private fun node(index: Int): Node<E>? {
        if (index < (len shr 1)) {
            var cur = head
            for (i in 0 until index) {
                cur = cur?.next
            }
            return cur
        } else {
            var cur = last
            for (i in (len - 1) downTo index + 1) {
                cur = cur?.prev
            }
            return cur
        }
    }

6.insert(index: Int,e: E)，从任意位置插入一个节点

override fun insert(index: Int, e: E) {
        if (index < 0 || index > len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        if (index == len) {
            linkLast(e)
        } else {
            linkBefore(node(index), e)
        }
        len++
    }
private fun linkLast(e: E) {
        var l = last
        val newNode = Node(null, last, e)
        last = newNode
        if (head != null) {
            l?.next = newNode
        } else {
            head = newNode
        }
    }
 private fun linkBefore(cur: Node<E>?, e: E) {
        val prev = cur?.prev

        val newNode = Node(cur, prev, e)
        cur?.prev = newNode
        if (prev != null) {
            prev.next = newNode
        } else {
            head = newNode
        }
    }

7.remove(index: Int)，任意位置删除一个节点

override fun remove(index: Int) {
        if (index < 0 || index >= len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        unlike(node(index))
        len--
    }
private fun unlike(cur: Node<E>?): E? {
        val value = cur?.value
        val prev = cur?.prev
        val next = cur?.next
        if (prev != null) {
            prev.next = next
        } else {
            head = next
        }
        if (next != null) {
            next.prev = prev
        } else {
            last = prev
        }
        return value
    }

8.完整Demo

package day1

class LinkedList<E> : LinkedListAction<E> {
    //头指针
    private var head: Node<E>? = null

    //优化时间复杂度
    private var last: Node<E>? = null

    //集合的长度
    private var len = 0

    override fun push(e: E) {
        linkLast(e)
        len++
    }

    private fun linkLast(e: E) {
        var l = last
        val newNode = Node(null, last, e)
        last = newNode
        if (head != null) {
            l?.next = newNode
        } else {
            head = newNode
        }
    }

    //找到对应index下标的节点。
    private fun node(index: Int): Node<E>? {
        if (index < (len shr 1)) {
            var cur = head
            for (i in 0 until index) {
                cur = cur?.next
            }
            return cur
        } else {
            var cur = last
            for (i in (len - 1) downTo index + 1) {
                cur = cur?.prev
            }
            return cur
        }
    }

    override fun size(): Int {
        return len
    }

    override fun getValue(index: Int): E? {
        if (index < 0 || index >= len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        return node(index)?.value
    }

    override fun insert(index: Int, e: E) {
        if (index < 0 || index > len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        if (index == len) {
            linkLast(e)
        } else {
            linkBefore(node(index), e)
        }
        len++
    }

    private fun linkBefore(cur: Node<E>?, e: E) {
        val prev = cur?.prev

        val newNode = Node(cur, prev, e)
        cur?.prev = newNode
        if (prev != null) {
            prev.next = newNode
        } else {
            head = newNode
        }
    }

    override fun remove(index: Int) {
        if (index < 0 || index >= len) {
            throw ArrayIndexOutOfBoundsException("数组越界.....")
        }
        unlike(node(index))
        len--
    }

    private fun unlike(cur: Node<E>?): E? {
        val value = cur?.value
        val prev = cur?.prev
        val next = cur?.next
        if (prev != null) {
            prev.next = next
        } else {
            head = next
        }
        if (next != null) {
            next.prev = prev
        } else {
            last = prev
        }
        return value
    }


}