leecode 1206｜跳表的设计

跳表

跳表，一种链表数据结构，其增删改茶的效率能和平衡树相媲美

leecode1206

可以看上面的那个动画，动画效果很贴切。

我简单讲讲它的机制吧，每个节点不单单是一个，测试好几层，然后同一层的节点和统一节点的next 采用单链表产生联系

最核心的东西在于find

这也是为什么单链表的增删改查，花费开销最多的地方。
在这里插入图片描述

那它是怎么查的？
我们已经知道了跳表的结构了，最底层肯定是最全的，如果暴力最底层，那就和单链表没什么区别了。

它的这个查恰巧结合了跳表的结构，如果在上面某个层找到了节点x 的pre那么接下来的操作都好办了。
那它是怎么找到节点x 的pre呢？
从最上层，依次找该节点的next 知道找到pre 如果在这一层还没找到(因为最后一个节点的next 为nullptr)，那么会在这个节点的下一层继续找同层找next。依此类推，最后肯定能找到的。

class Skiplist {
private:static const int MAX_LEVEL = 10;struct Node{int val;std::vector<Node*> ne;Node(int _val, int level):val(_val), ne(level, nullptr){};};int level;Node* head;float probability;int randomLevel(){int lvl = 1;while((float) std::rand() / RAND_MAX < probability && lvl < MAX_LEVEL){lvl++;}return lvl;}void find(int t, std::vector<Node*>& ns){Node* cur = head;for(int i = level - 1; i >= 0; i--){while(cur->ne[i] != nullptr && cur->ne[i]->val < t){cur = cur->ne[i];}ns[i] = cur;}}
public:Skiplist() :level(MAX_LEVEL), head(new Node(-1, MAX_LEVEL)), probability(0.5){std::srand(std::time(0));}bool search(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);Node* target = ns[0]->ne[0];return target != nullptr && target->val == t;}void add(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);int nodeLevel = randomLevel();Node* newNode = new Node(t, nodeLevel);for(int i = 0; i < nodeLevel; i++){newNode->ne[i] = ns[i]->ne[i];ns[i]->ne[i] = newNode;}}bool erase(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);Node* target = ns[0]->ne[0];if(target == nullptr || target->val != t){return false;}for(int i = 0; i < level && ns[i]->ne[i] == target; i++){ns[i]->ne[i] = ns[i]->ne[i]->ne[i];}delete target;return true;}~Skiplist(){Node* cur = head;while(cur){Node* next = cur->ne[0];delete cur;cur = next;}}
};/*** Your Skiplist object will be instantiated and called as such:* Skiplist* obj = new Skiplist();* bool param_1 = obj->search(target);* obj->add(num);* bool param_3 = obj->erase(num);*/

再贴一份，

#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>class Skiplist {
private:static const int MAX_LEVEL = 10;struct Node {int val;std::vector<Node*> ne;Node(int _val, int level) : val(_val), ne(level, nullptr) {}};int level;Node* head;float probability;int randomLevel() {int lvl = 1;while ((float)std::rand() / RAND_MAX < probability && lvl < MAX_LEVEL) {lvl++;}return lvl;}void find(int t, std::vector<Node*>& ns) {Node* cur = head;for (int i = level - 1; i >= 0; i--) {while (cur->ne[i] != nullptr && cur->ne[i]->val < t) {cur = cur->ne[i];}ns[i] = cur;}}public:Skiplist() : level(MAX_LEVEL), head(new Node(-1, MAX_LEVEL)), probability(0.5) {std::srand(std::time(0));}bool search(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);Node* target = ns[0]->ne[0];return target != nullptr && target->val == t;}void add(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);int nodeLevel = randomLevel();Node* newNode = new Node(t, nodeLevel);for (int i = 0; i < nodeLevel; i++) {newNode->ne[i] = ns[i]->ne[i];ns[i]->ne[i] = newNode;}}bool erase(int t) {std::vector<Node*> ns(level, nullptr);find(t, ns);Node* target = ns[0]->ne[0];if (target == nullptr || target->val != t) {return false;}for (int i = 0; i < level && ns[i]->ne[i] == target; i++) {ns[i]->ne[i] = ns[i]->ne[i]->ne[i];}delete target;return true;}~Skiplist() {Node* cur = head;while (cur) {Node* next = cur->ne[0];delete cur;cur = next;}}
};int main() {Skiplist skiplist;skiplist.add(1);skiplist.add(2);skiplist.add(3);std::cout << skiplist.search(1) << std::endl;  // returns truestd::cout << skiplist.search(4) << std::endl;  // returns falseskiplist.add(4);std::cout << skiplist.search(4) << std::endl;  // returns truestd::cout << skiplist.erase(4) << std::endl;   // returns truestd::cout << skiplist.search(4) << std::endl;  // returns falsereturn 0;
}