二叉排序树（BST）

Posted 2021-03-10 bingbug

二叉排序树对于任何一个非叶子节点都要求比左子节点大，比右子节点下，相同可放入左子节点或右子节点

对于删除情况，直接删除叶子节点和删除只有一颗子树的情况都比较好处理，对于第3种情况删除2棵子树详细记录一下

找到要删除的节点的父节点和他右子树找到最小值，最小值记录在临时变量里，删除最小节点，替换

public class BinarySortTreeDemo {

    public static void main(String[] args) {

        int[] arr = {7, 3, 10, 12, 5, 1, 9, 0};
        BinarySortTree binarySortTree = new BinarySortTree();
        for (int i = 0; i < arr.length; i++) {
            binarySortTree.add(new Node(arr[i]));
        }
        binarySortTree.delete(2);
        binarySortTree.delete(5);
        binarySortTree.delete(9);
        binarySortTree.delete(12);
        binarySortTree.delete(1);
        binarySortTree.delete(10);
        binarySortTree.delete(0);
        binarySortTree.delete(3);
        binarySortTree.delete(7);
        binarySortTree.infixOrder();
    }
}

class BinarySortTree {
    private Node root;

    public void add(Node node) {
        if (root == null) {
            root = node;
        } else {
            root.add(node);
        }
    }

    public void infixOrder() {
        if (root != null) {
            root.infixOrder();
        }
    }

    public Node search(int value) {
        if (root == null) {
            return null;
        } else {
            return root.search(value);
        }
    }

    public Node searchParent(int value) {
        if (root == null) {
            return null;
        } else {
            return root.searchParent(value);
        }
    }

    public int delRightTreeMin(Node node) {
        Node target = node;
        while (target.right != null) {
            target = target.right;
        }
        delete(target.value);
        return target.value;
    }

    public void delete(int value) {
        if (root == null) {
            return;
        } else {
            Node targetNode = search(value);
            if (targetNode == null) {
                return;
            }
            if (root.left == null && root.right == null) {
                root = null;
                return;
            }

            Node parent = searchParent(value);
            if (targetNode.left == null && targetNode.right == null) {
                if (parent.left != null && parent.left == targetNode) {
                    parent.left = null;
                } else if (parent.right != null && parent.right == targetNode) {
                    parent.right = null;
                }
            } else if (targetNode.left != null && targetNode.right != null) {
                int minVal = delRightTreeMin(targetNode.left);
                targetNode.value = minVal;
            } else {
                if (targetNode.left != null) {
                    if (parent != null) {
                        if (parent.left.value == value) {
                            parent.left = targetNode.left;
                        } else {
                            parent.right = targetNode.left;
                        }
                    } else {
                        root = targetNode.left;
                    }
                } else {
                    if (parent != null) {
                        if (parent.left.value == value) {
                            parent.left = targetNode.right;
                        } else {
                            parent.right = targetNode.right;
                        }
                    } else {
                        root = targetNode.right;
                    }
                }
            }
        }
    }
}

class Node {
    int value;
    Node left;
    Node right;

    public Node(int value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Node[" +
                "value=" + value +
                ‘]‘;
    }

    public void add(Node node) {
        if (node == null) {
            return;
        }
        if (node.value < this.value) {
            if (this.left == null) {
                this.left = node;
            } else {
                this.left.add(node);
            }
        } else {
            if (this.right == null) {
                this.right = node;
            } else {
                this.right.add(node);
            }
        }
    }

    public void infixOrder() {
        if (this.left != null) {
            this.left.infixOrder();
        }
        System.out.println(this);
        if (this.right != null) {
            this.right.infixOrder();
        }
    }

    public Node search(int value) {
        if (value == this.value) {
            return this;
        } else if (value < this.value) {
            if (this.left == null) {
                return null;
            }
            return this.left.search(value);
        } else {
            if (this.right == null) {
                return null;
            }
            return this.right.search(value);
        }
    }

    /**
     * @param value 要找的值
     * @return 要删除节点的父节点 没有返回null
     */
    public Node searchParent(int value) {
        if ((this.left != null && this.left.value == value) ||
                (this.right != null && this.right.value == value)) {
            return this;
        } else {
            if (value < this.value && this.left != null) {
                return this.left.searchParent(value);
            } else if (value >= this.value && this.left != null) {
                return this.right.searchParent(value);
            } else {
                return null;
            }
        }
    }
}