1、红黑树的属性
红黑树是一种二分查找树,与普通的二分查找树不同的一点是,红黑树的每个节点都有一个颜色(color)属性。该属性的值要么是红色,要么是黑色。
通过限制从根到叶子的任何简单路径上的节点颜色,红黑树确保没有比任何其他路径长两倍的路径,从而使树近似平衡。
假设红黑树节点的属性有键(key
)、颜色(color
)、左子节点(left
)、右子节点(right
),父节点(parent
)。
一棵红黑树必须满足下面有下面这些特性( 红黑树特性 ):
- 树中的每个节点要么是红色,要么是黑色;
- 根节点是黑色;
- 每个叶子节点(null)是黑色;
- 如果某节点是红色的,它的两个子节点都是黑色;
- 对于每个节点到后面任一叶子节点(null)的所有路径,都有相同数量的黑色节点。
为了在红黑树代码中处理边界条件方便,我们用一个哨兵变量代替null。对于一个红黑树tree
,哨兵变量RedBlackTree.NULL
(下文代码中)是一个和其它节点有同样属性的节点,它的颜色(color
)属性是黑色,其它属性可以任意取值。
我们使用哨兵变量是因为我们可以把一个节点node
的子节点null
当成一个普通节点。
在这里,我们使用哨兵变量RedBlackTree.NULL
代替树中所有的null
(所有的叶子节点及根节点的父节点)。
我们把从一个节点n(不包括)到任一叶子节点路径上的黑色节点的个数称为 黑色高度 ,用bh(n)表示。一棵红黑树的黑色高度是其根节点的黑色高度。
关于红黑树的搜索,求最小值,求最大值,求前驱,求后继这些操作的代码与二分查找树的这些操作的代码基本一致。可以在用java
实现二分查找树查看。
结合上文给出下面的代码。
用一个枚举类Color表示颜色:
public enum Color { Black("黑色"), Red("红色"); private String color; private Color(String color) { this.color = color; } @Override public String toString() { return color; } }
类Node表示节点:
public class Node { public int key; public Color color; public Node left; public Node right; public Node parent; public Node() { } public Node(Color color) { this.color = color; } public Node(int key) { this.key = key; this.color = Color.Red; } public int height() { return Math.max(left != RedBlackTree.NULL ? left.height() : 0, right != RedBlackTree.NULL ? right.height() : 0) + 1; } public Node minimum() { Node pointer = this; while (pointer.left != RedBlackTree.NULL) pointer = pointer.left; return pointer; } @Override public String toString() { String position = "null"; if (this.parent != RedBlackTree.NULL) position = this.parent.left == this ? "left" : "right"; return "[key: " + key + ", color: " + color + ", parent: " + parent.key + ", position: " + position + "]"; } }
类RedTreeNode表示红黑树:
public class RedBlackTree { // 表示哨兵变量 public final static Node NULL = new Node(Color.Black); public Node root; public RedBlackTree() { this.root = NULL; } }
2、旋转
红黑树的插入和删除操作,能改变红黑树的结构,可能会使它不再有前面所说的某些特性性。为了维持这些特性,我们需要改变树中某些节点的颜色和位置。
我们可以通过旋转改变节点的结构。主要有 左旋转
和 右旋转
两种方式。具体如下图所示。
左旋转:把一个节点n的右子节点right变为它的父节点,n变为right的左子节点,所以right不能为null。这时n的右指针空了出来,right的左子树被n挤掉,所以right原来的左子树称为n的右子树。
右旋转:把一个节点n的左子节点left变为它的父节点,n变为left的右子节点,所以left不能为null。这时n的左指针被空了出来,left的右子树被n挤掉,所以left原来的右子树被称为n的左子树。
可在RedTreeNode类中,加上如下实现代码:
public void leftRotate(Node node) { Node rightNode = node.right; node.right = rightNode.left; if (rightNode.left != RedBlackTree.NULL) rightNode.left.parent = node; rightNode.parent = node.parent; if (node.parent == RedBlackTree.NULL) this.root = rightNode; else if (node.parent.left == node) node.parent.left = rightNode; else node.parent.right = rightNode; rightNode.left = node; node.parent = rightNode; } public void rightRotate(Node node) { Node leftNode = node.left; node.left = leftNode.right; if (leftNode.right != RedBlackTree.NULL) leftNode.right.parent = node; leftNode.parent = node.parent; if (node.parent == RedBlackTree.NULL) { this.root = leftNode; } else if (node.parent.left == node) { node.parent.left = leftNode; } else { node.parent.right = leftNode; } leftNode.right = node; node.parent = leftNode; }
3、插入
红黑树的插入代码与二分查找树的插入代码非常相似。只不过红黑树的插入操作会改变红黑树的结构,使其不在有该有的特性。
在这里,新插入的节点默认是红色。
所以在插入节点之后,要有维护红黑树特性的代码。
public void insert(Node node) { Node parentPointer = RedBlackTree.NULL; Node pointer = this.root; while (this.root != RedBlackTree.NULL) { parentPointer = pointer; pointer = node.key < pointer.key ? pointer.left : pointer.right; } node.parent = parentPointer; if(parentPointer == RedBlackTree.NULL) { this.root = node; }else if(node.key < parentPointer.key) { parentPointer.left = node; }else { parentPointer.right = node; } node.left = RedBlackTree.NULL; node.right = RedBlackTree.NULL; node.color = Color.Red; // 维护红黑树属性的方法 this.insertFixUp(node); }
用上述方法插入一个新节点的时候,有两类情况会违反红黑树的特性。
- 当树中没有节点时,此时插入的节点称为根节点,而此节点的颜色为红色。
- 当新插入的节点成为一个红色节点的子节点时,此时存在一个红色结点有红色子节点的情况。
对于第一类情况,可以直接把根结点设置为黑色;而针对第二类情况,需要根据具体条件,做出相应的解决方案。
具体代码如下:
public void insertFixUp(Node node) { // 当node不是根结点,且node的父节点颜色为红色 while (node.parent.color == Color.Red) { // 先判断node的父节点是左子节点,还是右子节点,这不同的情况,解决方案也会不同 if (node.parent == node.parent.parent.left) { Node uncleNode = node.parent.parent.right; if (uncleNode.color == Color.Red) { // 如果叔叔节点是红色,则父父一定是黑色 // 通过把父父节点变成红色,父节点和兄弟节点变成黑色,然后在判断父父节点的颜色是否合适 uncleNode.color = Color.Black; node.parent.color = Color.Black; node.parent.parent.color = Color.Red; node = node.parent.parent; } else if (node == node.parent.right) { node = node.parent; this.leftRotate(node); } else { node.parent.color = Color.Black; node.parent.parent.color = Color.Red; this.rightRotate(node.parent.parent); } } else { Node uncleNode = node.parent.parent.left; if (uncleNode.color == Color.Red) { uncleNode.color = Color.Black; node.parent.color = Color.Black; node.parent.parent.color = Color.Red; node = node.parent.parent; } else if (node == node.parent.left) { node = node.parent; this.rightRotate(node); } else { node.parent.color = Color.Black; node.parent.parent.color = Color.Red; this.leftRotate(node.parent.parent); } } } // 如果之前树中没有节点,那么新加入的点就成了新结点,而新插入的结点都是红色的,所以需要修改。 this.root.color = Color.Black; }
下面的图分别对应第二类情况中的六种及相应处理结果。
情况1:
情况2:
情况3:
情况4:
情况5:
情况6:
4、删除
红黑树中节点的删除会使一个结点代替另外一个节点。所以先要实现这样的代码:
public void transplant(Node n1, Node n2) { if(n1.parent == RedBlackTree.NULL){ this.root = n2; }else if(n1.parent.left == n1) { n1.parent.left = n2; }else { n1.parent.right = n2; } n2.parent = n1.parent; }
红黑树的删除节点代码是基于二分查找树的删除节点代码而写的。
删除结点代码:
public void delete(Node node) { Node pointer1 = node; // 用于记录被删除的颜色,如果是红色,可以不用管,但如果是黑色,可能会破坏红黑树的属性 Color pointerOriginColor = pointer1.color; // 用于记录问题的出现点 Node pointer2; if (node.left == RedBlackTree.NULL) { pointer2 = node.right; this.transplant(node, node.right); } else if (node.right == RedBlackTree.NULL) { pointer2 = node.left; this.transplant(node, node.left); } else { // 如要删除的字节有两个子节点,则找到其直接后继(右子树最小值),直接后继节点没有非空左子节点。 pointer1 = node.right.minimum(); // 记录直接后继的颜色和其右子节点 pointerOriginColor = pointer1.color; pointer2 = pointer1.right; // 如果其直接后继是node的右子节点,不用进行处理 if (pointer1.parent == node) { pointer2.parent = pointer1; } else { // 否则,先把直接后继从树中提取出来,用来替换node this.transplant(pointer1, pointer1.right); pointer1.right = node.right; pointer1.right.parent = pointer1; } // 用node的直接后继替换node,继承node的颜色 this.transplant(node, pointer1); pointer1.left = node.left; pointer1.left.parent = pointer1; pointer1.color = node.color; } if (pointerOriginColor == Color.Black) { this.deleteFixUp(pointer2); } }
当被删除节点的颜色是黑色时需要调用方法维护红黑树的特性。
主要有两类情况:
- 当node是红色时,直接变成黑色即可。
- 当node是黑色时,需要调整红黑树结构。,
private void deleteFixUp(Node node) { // 如果node不是根节点,且是黑色 while (node != this.root && node.color == Color.Black) { // 如果node是其父节点的左子节点 if (node == node.parent.left) { // 记录node的兄弟节点 Node pointer1 = node.parent.right; // 如果他兄弟节点是红色 if (pointer1.color == Color.Red) { pointer1.color = Color.Black; node.parent.color = Color.Red; leftRotate(node.parent); pointer1 = node.parent.right; } if (pointer1.left.color == Color.Black && pointer1.right.color == Color.Black) { pointer1.color = Color.Red; node = node.parent; } else if (pointer1.right.color == Color.Black) { pointer1.left.color = Color.Black; pointer1.color = Color.Red; rightRotate(pointer1); pointer1 = node.parent.right; } else { pointer1.color = node.parent.color; node.parent.color = Color.Black; pointer1.right.color = Color.Black; leftRotate(node.parent); node = this.root; } } else { // 记录node的兄弟节点 Node pointer1 = node.parent.left; // 如果他兄弟节点是红色 if (pointer1.color == Color.Red) { pointer1.color = Color.Black; node.parent.color = Color.Red; rightRotate(node.parent); pointer1 = node.parent.left; } if (pointer1.right.color == Color.Black && pointer1.left.color == Color.Black) { pointer1.color = Color.Red; node = node.parent; } else if (pointer1.left.color == Color.Black) { pointer1.right.color = Color.Black; pointer1.color = Color.Red; leftRotate(pointer1); pointer1 = node.parent.left; } else { pointer1.color = node.parent.color; node.parent.color = Color.Black; pointer1.left.color = Color.Black; rightRotate(node.parent); node = this.root; } } } node.color = Color.Black; }
对第二类情况,有下面8种:
情况1:
情况2:
情况3:
情况4:
情况5:
情况6:
情况7:
情况8:
5、所有代码
public enum Color { Black("黑色"), Red("红色"); private String color; private Color(String color) { this.color = color; } @Override public String toString() { return color; } } public class Node { public int key; public Color color; public Node left; public Node right; public Node parent; public Node() { } public Node(Color color) { this.color = color; } public Node(int key) { this.key = key; this.color = Color.Red; } /** * 求在树中节点的高度 * * @return */ public int height() { return Math.max(left != RedBlackTree.NULL ? left.height() : 0, right != RedBlackTree.NULL ? right.height() : 0) + 1; } /** * 在以该节点为根节点的树中,求最小节点 * * @return */ public Node minimum() { Node pointer = this; while (pointer.left != RedBlackTree.NULL) pointer = pointer.left; return pointer; } @Override public String toString() { String position = "null"; if (this.parent != RedBlackTree.NULL) position = this.parent.left == this ? "left" : "right"; return "[key: " + key + ", color: " + color + ", parent: " + parent.key + ", position: " + position + "]"; } } import java.util.LinkedList; import java.util.Queue; public class RedBlackTree { public final static Node NULL = new Node(Color.Black); public Node root; public RedBlackTree() { this.root = NULL; } /** * 左旋转 * * @param node */ public void leftRotate(Node node) { Node rightNode = node.right; node.right = rightNode.left; if (rightNode.left != RedBlackTree.NULL) rightNode.left.parent = node; rightNode.parent = node.parent; if (node.parent == RedBlackTree.NULL) this.root = rightNode; else if (node.parent.left == node) node.parent.left = rightNode; else node.parent.right = rightNode; rightNode.left = node; node.parent = rightNode; } /** * 右旋转 * * @param node */ public void rightRotate(Node node) { Node leftNode = node.left; node.left = leftNode.right; if (leftNode.right != RedBlackTree.NULL) leftNode.right.parent = node; leftNode.parent = node.parent; if (node.parent == RedBlackTree.NULL) { this.root = leftNode; } else if (node.parent.left == node) { node.parent.left = leftNode; } else { node.parent.right = leftNode; } leftNode.right = node; node.parent = leftNode; } public void insert(Node node) { Node parentPointer = RedBlackTree.NULL; Node pointer = this.root; while (pointer != RedBlackTree.NULL) { parentPointer = pointer; pointer = node.key < pointer.key ? pointer.left : pointer.right; } node.parent = parentPointer; if (parentPointer == RedBlackTree.NULL) { this.root = node; } else if (node.key < parentPointer.key) { parentPointer.left = node; } else { parentPointer.right = node; } node.left = RedBlackTree.NULL; node.right = RedBlackTree.NULL; node.color = Color.Red; this.insertFixUp(node); } private void insertFixUp(Node node) { // 当node不是根结点,且node的父节点颜色为红色 while (node.parent.color == Color.Red) { // 先判断node的父节点是左子节点,还是右子节点,这不同的情况,解决方案也会不同 if (node.parent == node.parent.parent.left) { Node uncleNode = node.parent.parent.right; if (uncleNode.color == Color.Red) { // 如果叔叔节点是红色,则父父一定是黑色 // 通过把父父节点变成红色,父节点和兄弟节点变成黑色,然后在判断父父节点的颜色是否合适 uncleNode.color = Color.Black; node.parent.color = Color.Black; node.parent.parent.color = Color.Red; node = node.parent.parent; } else if (node == node.parent.right) { // node是其父节点的右子节点,且叔叔节点是黑色 // 对node的父节点进行左旋转 node = node.parent; this.leftRotate(node); } else { // node如果叔叔节点是黑色,node是其父节点的左子节点,父父节点是黑色 // 把父节点变成黑色,父父节点变成红色,对父父节点进行右旋转 node.parent.color = Color.Black; node.parent.parent.color = Color.Red; this.rightRotate(node.parent.parent); } } else { Node uncleNode = node.parent.parent.left; if (uncleNode.color == Color.Red) { uncleNode.color = Color.Black; node.parent.color = Color.Black; node.parent.parent.color = Color.Red; node = node.parent.parent; } else if (node == node.parent.left) { node = node.parent; this.rightRotate(node); } else { node.parent.color = Color.Black; node.parent.parent.color = Color.Red; this.leftRotate(node.parent.parent); } } } // 如果之前树中没有节点,那么新加入的点就成了新结点,而新插入的结点都是红色的,所以需要修改。 this.root.color = Color.Black; } /** * n2替代n1 * * @param n1 * @param n2 */ private void transplant(Node n1, Node n2) { if (n1.parent == RedBlackTree.NULL) { // 如果n1是根节点 this.root = n2; } else if (n1.parent.left == n1) { // 如果n1是其父节点的左子节点 n1.parent.left = n2; } else { // 如果n1是其父节点的右子节点 n1.parent.right = n2; } n2.parent = n1.parent; } /** * 删除节点node * * @param node */ public void delete(Node node) { Node pointer1 = node; // 用于记录被删除的颜色,如果是红色,可以不用管,但如果是黑色,可能会破坏红黑树的属性 Color pointerOriginColor = pointer1.color; // 用于记录问题的出现点 Node pointer2; if (node.left == RedBlackTree.NULL) { pointer2 = node.right; this.transplant(node, node.right); } else if (node.right == RedBlackTree.NULL) { pointer2 = node.left; this.transplant(node, node.left); } else { // 如要删除的字节有两个子节点,则找到其直接后继(右子树最小值),直接后继节点没有非空左子节点。 pointer1 = node.right.minimum(); // 记录直接后继的颜色和其右子节点 pointerOriginColor = pointer1.color; pointer2 = pointer1.right; // 如果其直接后继是node的右子节点,不用进行处理 if (pointer1.parent == node) { pointer2.parent = pointer1; } else { // 否则,先把直接后继从树中提取出来,用来替换node this.transplant(pointer1, pointer1.right); pointer1.right = node.right; pointer1.right.parent = pointer1; } // 用node的直接后继替换node,继承node的颜色 this.transplant(node, pointer1); pointer1.left = node.left; pointer1.left.parent = pointer1; pointer1.color = node.color; } if (pointerOriginColor == Color.Black) { this.deleteFixUp(pointer2); } } /** * The procedure RB-DELETE-FIXUP restores properties 1, 2, and 4 * * @param node */ private void deleteFixUp(Node node) { // 如果node不是根节点,且是黑色 while (node != this.root && node.color == Color.Black) { // 如果node是其父节点的左子节点 if (node == node.parent.left) { // 记录node的兄弟节点 Node pointer1 = node.parent.right; // 如果node兄弟节点是红色 if (pointer1.color == Color.Red) { pointer1.color = Color.Black; node.parent.color = Color.Red; leftRotate(node.parent); pointer1 = node.parent.right; } if (pointer1.left.color == Color.Black && pointer1.right.color == Color.Black) { pointer1.color = Color.Red; node = node.parent; } else if (pointer1.right.color == Color.Black) { pointer1.left.color = Color.Black; pointer1.color = Color.Red; rightRotate(pointer1); pointer1 = node.parent.right; } else { pointer1.color = node.parent.color; node.parent.color = Color.Black; pointer1.right.color = Color.Black; leftRotate(node.parent); node = this.root; } } else { // 记录node的兄弟节点 Node pointer1 = node.parent.left; // 如果他兄弟节点是红色 if (pointer1.color == Color.Red) { pointer1.color = Color.Black; node.parent.color = Color.Red; rightRotate(node.parent); pointer1 = node.parent.left; } if (pointer1.right.color == Color.Black && pointer1.left.color == Color.Black) { pointer1.color = Color.Red; node = node.parent; } else if (pointer1.left.color == Color.Black) { pointer1.right.color = Color.Black; pointer1.color = Color.Red; leftRotate(pointer1); pointer1 = node.parent.left; } else { pointer1.color = node.parent.color; node.parent.color = Color.Black; pointer1.left.color = Color.Black; rightRotate(node.parent); node = this.root; } } } node.color = Color.Black; } private void innerWalk(Node node) { if (node != NULL) { innerWalk(node.left); System.out.println(node); innerWalk(node.right); } } /** * 中序遍历 */ public void innerWalk() { this.innerWalk(this.root); } /** * 层次遍历 */ public void print() { Queue<Node> queue = new LinkedList<>(); queue.add(this.root); while (!queue.isEmpty()) { Node temp = queue.poll(); System.out.println(temp); if (temp.left != NULL) queue.add(temp.left); if (temp.right != NULL) queue.add(temp.right); } } // 查找 public Node search(int key) { Node pointer = this.root; while (pointer != NULL && pointer.key != key) { pointer = pointer.key < key ? pointer.right : pointer.left; } return pointer; } }
6、演示
演示代码:
public class Test01 { public static void main(String[] args) { int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8 }; RedBlackTree redBlackTree = new RedBlackTree(); for (int i = 0; i < arr.length; i++) { redBlackTree.insert(new Node(arr[i])); } System.out.println("树的高度: " + redBlackTree.root.height()); System.out.println("左子树的高度: " + redBlackTree.root.left.height()); System.out.println("右子树的高度: " + redBlackTree.root.right.height()); System.out.println("层次遍历"); redBlackTree.print(); // 要删除节点 Node node = redBlackTree.search(4); redBlackTree.delete(node); System.out.println("树的高度: " + redBlackTree.root.height()); System.out.println("左子树的高度: " + redBlackTree.root.left.height()); System.out.println("右子树的高度: " + redBlackTree.root.right.height()); System.out.println("层次遍历"); redBlackTree.print(); } }
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