目录
一.红黑树
二.红黑树的实现
1.红黑树节点的定义
2.红黑树的插入
3.红黑树的遍历
4.检测红黑树
5.红黑树的查找
6.红黑树的性能
三.整体代码
1.RBTree.h
2.RBTree.cpp
一.红黑树
1.红黑树的概念
红黑树,是一种二叉搜索树,但在每个结点上增加一个存储位表示结点的颜色,可以是Red或 Black。 通过对任何一条从根到叶子的路径上各个结点着色方式的限制,红黑树确保没有一条路径会比其他路径长出俩倍,因而是接近平衡的
2.红黑树的性质
- 每个结点不是红色就是黑色
- 根节点是黑色的
- 如果一个节点是红色的,则它的两个孩子结点是黑色的
- 对于每个结点,从该结点到其所有后代叶结点的简单路径上,均包含相同数目的黑色结点
- 每个叶子结点都是黑色的(此处的叶子结点指的是空结点)
思考:为什么满足上面的性质,红黑树就能保证:其最长路径中节点个数不会超过最短路径节点 个数的两倍?
因为最短路径为全黑,最长路径为1红1黑,路径中的黑色节点数相同,中间可以插入红色节点
二.红黑树的实现
1.红黑树节点的定义
enum Colour
{BLACK,RED,
};template<class K,class V>
struct RBTreeNode
{RBTreeNode* _left;RBTreeNode* _right;RBTreeNode* _parent;pair<K, V> _kv;Colour _col;RBTreeNode(const pair<K, V>& kv) :_left(nullptr), _right(nullptr), _parent(nullptr), _kv(kv), _col(RED) { };
};
2.红黑树的插入
首先按照二叉搜索树的规则进行插入
//按照搜索树的规则插入
if (_root == nullptr)
{_root = new Node(kv);_root->_col = BLACK;return true;
}Node* parent = nullptr;
Node* cur = _root;
while (cur)
{if (cur->_kv.first < kv.first){parent = cur;cur = cur->_right;}else if (cur->_kv.first > kv.first){parent = cur;cur = cur->_left;}else{return false;}
}cur = new Node(kv);
if (parent->_kv.first < kv.first)
{parent->_right = cur;cur->_parent = parent;
}
else
{parent->_left = cur;cur->_parent = parent;
}//新增节点红的
cur->_col = RED;
这里为什么将新增节点的颜色设置为红的?
新增节点颜色的选择主要看的是对性质的破坏程度,选择红的,会破坏不能有连续的红色节点性质,而选择黑的,因为每条路径的黑色节点数需要数目相同,设为黑的每一条都需要改变,相比较之下,破坏不能有连续红色节点的性质较为轻
然后检测新节点插入后,红黑树的性质是否造到破坏
因为新节点的默认颜色是红色,因此:如果其双亲节点的颜色是黑色,没有违反红黑树任何 性质,则不需要调整;但当新插入节点的双亲节点颜色为红色时,就违反了性质不能有连在一起的红色节点,此时需要对红黑树分情况来讨论:
cur为当前节点,p为父节点,g为祖父节点,u为叔叔节点
情况一: cur为红,p为红,g为黑,u存在且为红
解决方式:将p,u改为黑,g改为红
注意:如果g为根,调整完后将g变为黑色
如果g是子树,g一定有双亲,如果为红色,继续向上调整
//情况一:uncle存在且为红if (uncle && uncle->_col == RED){parent->_col = uncle->_col = BLACK;grandfather->_col = RED;//继续向上处理cur = grandfather;parent = cur->_parent;}
情况二: cur为红,p为红,g为黑,u不存在/u存在且为黑
u的情况有两种:
- 如果u不存在,则cur一定为新增节点,因为如果cur不是新增的,那么cur和p一定有一个为黑的,不满足每条路径上黑色节点数目相同的性质
- 如果u存在,为黑色,那么cur原来的颜色一定为黑色,现在是红的是因为cur的子树调整过程中将cur的颜色由黑色变为红色
如何调整?
- p为g的左孩子,cur为p的左孩子,进行右单旋
- p为g的右孩子,cur为p的右孩子,进行左单旋
- 然后将p变黑,g变红
红黑树的左单旋,右单旋与AVL树的一样,只是没有平衡因子的调整,在这里直接给出
//左单旋void RotateL(Node* parent){Node* subR = parent->_right;Node* subRL = subR->_left;parent->_right = subRL;if (subRL)subRL->_parent = parent;subR->_left = parent;Node* ppNode = parent->_parent;parent->_parent = subR;//原来parent为根,现在subR为根//parent为树的子树,sunR替代parentif (_root == parent){_root = subR;subR->_parent = nullptr;}else{if (ppNode->_left == parent)ppNode->_left = subR;elseppNode->_right = subR;subR->_parent = ppNode;}}//右单旋void RotateR(Node* parent){Node* subL = parent->_left;Node* subLR = subL->_right;parent->_left = subLR;if (subLR)subLR->_parent = parent;subL->_right = parent;Node* ppNode = parent->_parent;parent->_parent = subL;if (_root == parent){_root = subL;subL->_parent = nullptr;}else{if (ppNode->_left == parent)ppNode->_left = subL;elseppNode->_right = subL;subL->_parent = ppNode;}}
情况三: cur为红,p为红,g为黑,u不存在/u存在且为黑
如何调整?
- p为g的左孩子,cur为p的右孩子,对p进行左单旋,转化为情况二,再对g进行右单旋
- p为g的右孩子,cur为p的左孩子,对p进行右单旋,转化为情况二,再对g进行左单旋
三种情况的插入实现如下
bool Insert(const pair<K, V>& kv){//按照搜索树的规则插入if (_root == nullptr){_root = new Node(kv);_root->_col = BLACK;return true;}Node* parent = nullptr;Node* cur = _root;while (cur){if (cur->_kv.first < kv.first){parent = cur;cur = cur->_right;}else if (cur->_kv.first > kv.first){parent = cur;cur = cur->_left;}else{return false;}}cur = new Node(kv);if (parent->_kv.first < kv.first){parent->_right = cur;cur->_parent = parent;}else{parent->_left = cur;cur->_parent = parent;}//新增节点红的cur->_col = RED;while (parent && parent->_col == RED){//红黑树的关键看叔叔Node* grandfather = parent->_parent;if (grandfather->_left == parent){Node* uncle = grandfather->_right;//情况一:uncle存在且为红if (uncle && uncle->_col == RED){parent->_col = uncle->_col = BLACK;grandfather->_col = RED;//继续向上处理cur = grandfather;parent = cur->_parent;}//情况二或情况三:uncle不存在或者uncle存在且为黑else{//情况三:双旋->变为单旋if (cur == parent->_right){RotateL(parent);swap(parent, cur);}//第二种情况(有可能为第三种情况变化而来)RotateR(grandfather);grandfather->_col = RED;parent->_col = BLACK;break;}}else{Node* uncle = grandfather->_left;//情况一:uncle存在且为红if (uncle && uncle->_col == RED){parent->_col = uncle->_col = BLACK;grandfather->_col = RED;//继续向上处理cur = grandfather;parent = cur->_parent;}//情况二或情况三:uncle不存在或者uncle存在且为黑else{//情况三:双旋->变为单旋if (cur == parent->_left){RotateR(parent);swap(parent, cur);}//第二种情况(有可能为第三种情况变化而来)RotateL(grandfather);grandfather->_col = RED;parent->_col = BLACK;break;}}}_root->_col = BLACK;return true;}
3.红黑树的遍历
void _InOrder(Node* root){if (root == nullptr)return;_InOrder(root->_left);cout << root->_kv.first << ":" << root->_kv.second << endl;_InOrder(root->_right);}void InOrder(){_InOrder(_root);}
4.检测红黑树
bool IsValidRBTree()
{Node* pRoot = _root;// 空树也是红黑树if (nullptr == pRoot)return true;// 检测根节点是否满足情况if (BLACK != pRoot->_col){cout << "违反红黑树性质:根节点必须为黑色" << endl;return false;}// 获取任意一条路径中黑色节点的个数size_t blackCount = 0; Node* pCur = pRoot;while (pCur){if (BLACK == pCur->_col)blackCount++;pCur = pCur->_left;}// 检测是否满足红黑树的性质,k用来记录路径中黑色节点的个数size_t k = 0;return _IsValidRBTree(pRoot, k, blackCount);
}bool _IsValidRBTree(Node* pRoot, size_t k, const size_t blackCount)
{//走到null之后,判断k和black是否相等if (nullptr == pRoot){if (k != blackCount){cout << "违反性质:每条路径中黑色节点的个数必须相同" << endl;return false;}return true;}// 统计黑色节点的个数if (BLACK == pRoot->_col)k++;// 检测当前节点与其双亲是否都为红色Node* pParent = pRoot->_parent;if (pParent && RED == pParent->_col && RED == pRoot->_col){cout << "违反性质:没有连在一起的红色节点" << endl;return false;}return _IsValidRBTree(pRoot->_left, k, blackCount) &&_IsValidRBTree(pRoot->_right, k, blackCount);
}
5.红黑树的查找
红黑树的查找与搜索树相同,大的向右找,小的向左找
Node* Find(const K& key){Node* cur = _root;while (cur){if (cur->_kv.first < key){cur = cur->_right;}else if (cur->_kv.first > key){cur = cur->_left;}else{return cur;}}return nullptr;}
6.红黑树的性能
红黑树和AVL树都是高效的平衡二叉树,增删改查的时间复杂度都是O(log2N),红黑树最短路径O(log2N),最长路径2*O(log2N),红黑树不追求绝对平衡,其只需保证最长路径不超过最短路径的2倍,相对而言,降低了插入和旋转的次数, 所以在经常进行增删的结构中性能比AVL树更优,而且红黑树实现比较简单,所以实际运用中红黑树更多
红黑树的性能与AVL树差了基本两倍,但是我们认为他们基本相同,为什么?
因为现在硬件的运算速度非常快,之间基本没有差异,log2N和2*log2N差别不大了
可以通过以下代码测试性能
void Testtime()
{const int n = 1000000;vector<int> v;v.reserve(n);srand(time(0));for (size_t i = 0; i < n; ++i){v.push_back(rand());}RBTree<int, int> rbtree;size_t begin1 = clock();for (auto e : v){rbtree.Insert(make_pair(e, e));}size_t end1 = clock();cout << end1 - begin1 << endl;
}
void Testtime()
{const int n = 1000000;vector<int> v;v.reserve(n);srand(time(0));for (size_t i = 0; i < n; ++i){v.push_back(rand());}AVLTree<int, int> avltree;size_t begin1 = clock();for (auto e : v){avltree.Insert(make_pair(e, e));}size_t end1 = clock();cout << end1 - begin1 << endl;
}
可以看到相同的100w个数据,红黑树189,AVL树176,他们之间差距并不是很大
三.整体代码
1.RBTree.h
#pragma onceenum Colour
{BLACK,RED,
};template<class K,class V>
struct RBTreeNode
{RBTreeNode* _left;RBTreeNode* _right;RBTreeNode* _parent;pair<K, V> _kv;Colour _col;RBTreeNode(const pair<K, V>& kv) :_left(nullptr), _right(nullptr), _parent(nullptr), _kv(kv), _col(RED) { };
};template<class K,class V>
class RBTree
{typedef RBTreeNode<K, V> Node;
public:bool Insert(const pair<K, V>& kv){//按照搜索树的规则插入if (_root == nullptr){_root = new Node(kv);_root->_col = BLACK;return true;}Node* parent = nullptr;Node* cur = _root;while (cur){if (cur->_kv.first < kv.first){parent = cur;cur = cur->_right;}else if (cur->_kv.first > kv.first){parent = cur;cur = cur->_left;}else{return false;}}cur = new Node(kv);if (parent->_kv.first < kv.first){parent->_right = cur;cur->_parent = parent;}else{parent->_left = cur;cur->_parent = parent;}//新增节点红的cur->_col = RED;while (parent && parent->_col == RED){//红黑树的关键看叔叔Node* grandfather = parent->_parent;if (grandfather->_left == parent){Node* uncle = grandfather->_right;//情况一:uncle存在且为红if (uncle && uncle->_col == RED){parent->_col = uncle->_col = BLACK;grandfather->_col = RED;//继续向上处理cur = grandfather;parent = cur->_parent;}//情况二或情况三:uncle不存在或者uncle存在且为黑else{//情况三:双旋->变为单旋if (cur == parent->_right){RotateL(parent);swap(parent, cur);}//第二种情况(有可能为第三种情况变化而来)RotateR(grandfather);grandfather->_col = RED;parent->_col = BLACK;break;}}else{Node* uncle = grandfather->_left;//情况一:uncle存在且为红if (uncle && uncle->_col == RED){parent->_col = uncle->_col = BLACK;grandfather->_col = RED;//继续向上处理cur = grandfather;parent = cur->_parent;}//情况二或情况三:uncle不存在或者uncle存在且为黑else{//情况三:双旋->变为单旋if (cur == parent->_left){RotateR(parent);swap(parent, cur);}//第二种情况(有可能为第三种情况变化而来)RotateL(grandfather);grandfather->_col = RED;parent->_col = BLACK;break;}}}_root->_col = BLACK;return true;}//左单旋void RotateL(Node* parent){Node* subR = parent->_right;Node* subRL = subR->_left;parent->_right = subRL;if (subRL)subRL->_parent = parent;subR->_left = parent;Node* ppNode = parent->_parent;parent->_parent = subR;//原来parent为根,现在subR为根//parent为树的子树,sunR替代parentif (_root == parent){_root = subR;subR->_parent = nullptr;}else{if (ppNode->_left == parent)ppNode->_left = subR;elseppNode->_right = subR;subR->_parent = ppNode;}}//右单旋void RotateR(Node* parent){Node* subL = parent->_left;Node* subLR = subL->_right;parent->_left = subLR;if (subLR)subLR->_parent = parent;subL->_right = parent;Node* ppNode = parent->_parent;parent->_parent = subL;if (_root == parent){_root = subL;subL->_parent = nullptr;}else{if (ppNode->_left == parent)ppNode->_left = subL;elseppNode->_right = subL;subL->_parent = ppNode;}}void _InOrder(Node* root){if (root == nullptr)return;_InOrder(root->_left);cout << root->_kv.first << ":" << root->_kv.second << endl;_InOrder(root->_right);}void InOrder(){_InOrder(_root);}bool IsValidRBTree(){Node* pRoot = _root;// 空树也是红黑树if (nullptr == pRoot)return true;// 检测根节点是否满足情况if (BLACK != pRoot->_col){cout << "违反红黑树性质:根节点必须为黑色" << endl;return false;}// 获取任意一条路径中黑色节点的个数size_t blackCount = 0; Node* pCur = pRoot;while (pCur){if (BLACK == pCur->_col)blackCount++;pCur = pCur->_left;}// 检测是否满足红黑树的性质,k用来记录路径中黑色节点的个数size_t k = 0;return _IsValidRBTree(pRoot, k, blackCount);}bool _IsValidRBTree(Node* pRoot, size_t k, const size_t blackCount){//走到null之后,判断k和black是否相等if (nullptr == pRoot){if (k != blackCount){cout << "违反性质:每条路径中黑色节点的个数必须相同" << endl;return false;}return true;}// 统计黑色节点的个数if (BLACK == pRoot->_col)k++;// 检测当前节点与其双亲是否都为红色Node* pParent = pRoot->_parent;if (pParent && RED == pParent->_col && RED == pRoot->_col){cout << "违反性质:没有连在一起的红色节点" << endl;return false;}return _IsValidRBTree(pRoot->_left, k, blackCount) &&_IsValidRBTree(pRoot->_right, k, blackCount);}Node* Find(const K& key){Node* cur = _root;while (cur){if (cur->_kv.first < key){cur = cur->_right;}else if (cur->_kv.first > key){cur = cur->_left;}else{return cur;}}return nullptr;}
private:Node* _root = nullptr;
};void TestRBTree()
{int a[] = { 4,5,7,8,1,2,3,9,10 };RBTree<int, int> r;for (auto e : a){r.Insert(make_pair(e, e));}r.InOrder();cout << r.IsValidRBTree() << endl;
}void Testtime()
{const int n = 1000000;vector<int> v;v.reserve(n);srand(time(0));for (size_t i = 0; i < n; ++i){v.push_back(rand());}RBTree<int, int> rbtree;size_t begin1 = clock();for (auto e : v){rbtree.Insert(make_pair(e, e));}size_t end1 = clock();cout << end1 - begin1 << endl;
}
2.RBTree.cpp
#include<iostream>
#include<vector>
#include<time.h>
using namespace std;
#include"RBTree.h"int main()
{TestRBTree();Testtime();return 0;
}