我正在尝试为自己的学习编写一个红黑树的实现，现在我已经盯着这几天了。
有谁可以帮我弄清楚如何让双旋转案例正常工作？如果你在浏览片段时发现其他任何糟糕的东西，请随意让我觉得自己像个白痴。
感谢您的帮助。
重新平衡功能
int impl_rbtree_rebalance (xs_rbtree_node *node)
{
check_mem(node);
xs_rbtree_node *p = node->parent;
if (!p) return 0;
if (p->color == BLACK) return 0;
xs_rbtree_node *gp = p->parent;
if (!gp) return 0;
xs_rbtree_node *uncle;
int is_parent_left_child;
/* check if parent is left or right child */
if (p == gp->left) {
uncle = gp->right;
is_parent_left_child = 1;
} else {
uncle = gp->left;
is_parent_left_child = 0;
}
if (uncle && uncle->color == RED) {
p->color = uncle->color = BLACK;
gp->color = RED;
} else { /* uncle is black */
if (gp->parent == NULL) return 0;
if (node == p->left) {
if (is_parent_left_child == 0) {
/* Double rotation logic */
} else {/* parent is left child */
gp->color = RED;
gp->left->color = BLACK;
impl_rbtree_rr(&gp);
}
} else { /* node is right child */
if (is_parent_left_child == 1) {
/* Double rotation logic */
} else { /* parent is right child */
gp->color = RED;
gp->right->color = BLACK;
impl_rbtree_rl(&gp);
}
}
}
return 0;
}
相关功能
xs_rbtree_node *impl_rbtree_node_alloc (xs_rbtree_node *parent, void *val)
{
xs_rbtree_node *n = malloc(sizeof(xs_rbtree_node));
n->parent = parent;
n->val = val;
n->left = n->right = NULL;
n->color = (parent == NULL) ? BLACK : RED;
return n;
}
void rbtree_insert (xs_rbtree_ *tree, void *val)
{
check_mem(tree);
check_mem(val);
tree->root = impl_rbtree_insert(tree->cmp, NULL, tree->root, val);
tree->root->color = BLACK;
}
xs_rbtree_node *impl_rbtree_insert (xs_tree_cmp cmp, xs_rbtree_node *parent, xs_rbtree_node *node, void *val)
{
check_mem(cmp);
check_mem(val);
if (!node) {
node = impl_rbtree_node_alloc(parent, val);
} else if (cmp(node->val, val) < 0) {
/* node->val < val */
check_mem(node);
node->right = impl_rbtree_insert(cmp, node, node->right, val);
impl_rbtree_rebalance(node->right);
} else if (cmp(node->val, val) > 0) {
/* node->val > val */
check_mem(node);
node->left = impl_rbtree_insert(cmp, node, node->left, val);
impl_rbtree_rebalance(node->left);
}
/* ignoring values that are equal */
return node;
}
轮换功能
#include <xs/base/bstree.h>
void impl_tree_rr(xs_tree_node **node)
{
check_mem(*node);
check_mem((*node)->left);
xs_tree_node *k1, *k2;
k2 = *node;
k1 = k2->left;
k2->left = k1->right;
k1->right = k2;
k1->parent = k2->parent;
k2->parent = k1;
*node = k1;
}
void impl_tree_rl(xs_tree_node **node)
{
check_mem(*node);
check_mem((*node)->right);
xs_tree_node *k1, *k2;
k2 = *node;
k1 = k2->right;
k2->right = k1->left;
k1->left = k2;
k1->parent = k2->parent;
k2->parent = k1;
*node = k1;
}
void impl_tree_drr(xs_tree_node **node)
{
check_mem(*node);
impl_tree_rl(&((*node)->left));
impl_tree_rr(node);
}
void impl_tree_drl(xs_tree_node **node)
{
check_mem(*node);
impl_tree_rr(&((*node)->right));
impl_tree_rl(node);
}
RBT定义
typedef struct xs_rbtree_node xs_rbtree_node;
typedef struct xs_rbtree_ xs_rbtree_;
typedef enum { RED, BLACK } impl_rbtree_color;
struct xs_rbtree_node {
xs_rbtree_node *left;
xs_rbtree_node *right;
xs_rbtree_node *parent;
void *val;
impl_rbtree_color color;
};
struct xs_rbtree_ {
xs_rbtree_node *root;
xs_tree_cmp cmp;
};
答案 0 :(得分：0)
与AVL树相比，在Red Black树中两次旋转有点棘手，原因是在RB树中存在父指针。 在旋转树时，我们也需要调整父指针。 我将通过一个例子来演示它。下面的树是初始树
20 / \ 10 30 / \ 3 15 / \ 12 18
然后向右旋转一个
10 / \ 3 20 / \ 15 30 / \ 12 18我们在那里观察了两件事。 1.根已更改。 2. 3个节点的父指针已更改（10，20，15），即。用于新的根，旧的根和新的根的右子。这对于 好吧，轮换案件。这是为了确保顺序 旋转发生后，遍历将保持不变。
现在看看我们如何逐步旋转。
public Node rotateRight() {
if(root.left == null) {
System.out.println("Cannot be rotated Right");
} else {
Node newRoot = root.left; // Assign new root.
Node orphaned = newRoot.right; // Store ref to the right child of new root.
newRoot.parent = root.parent; // new root parent point to old root parent.
root.parent = newRoot; // new root becomes parent of old root.
newRoot.right = root; // old root becomes right child of new root
root.left = orphaned;
if (orphaned != null) {
orphaned.parent = root;
}
root = newRoot;
}
return root;
}
尝试几次在纸上执行此操作，这样看起来会更简单。 希望这会有所帮助。
回到RB树。以上实现将应用于我们在平衡过程中所做的两个轮换。 （让我们接受正确的案例）
当我们有3代节点时，一个祖父，一个父亲和一个 被插入的孩子。 1.当我们有RR或LL配置时，不要交换颜色 2.使用RL和LR，我们旋转祖父，我们交换爷爷和父亲的颜色，但是当旋转父母时，我们不尝试交换 颜色。目的只是使它们进入RR或LL配置。
a. We need to see if the grandpa is right or left child of its parent and assign the root accordingly. b. If the grandpa has no parent means we are doing rotation at the level of tree's root, then we reassign the root of the tree.
我实现RB树的代码段。
temp is the new node which is added.
// if new node is the right child AND parent is right child
else if(temp.parent.right == temp && grandPa!=null && grandPa.right == temp.parent) {
// If becomes a right-right case
Boolean isLeft = isLeftChild(grandPa);
if(isLeft == null) {
// Grandpa has no parent, reassign root.
root = rotateLeft(grandPa,true);
}
else if(isLeft) {
grandPa.parent.left = rotateLeft(grandPa,true);
} else {
grandPa.parent.right = rotateLeft(grandPa,true);
}
}