// File: binary_search_tree.go
// Created Time: 2022-11-26
// Author: Reanon (793584285@qq.com)

package chapter_tree

import (
	"sort"

	. "github.com/krahets/hello-algo/pkg"
)

type BinarySearchTree struct {
	root *TreeNode
}

func NewBinarySearchTree(nums []int) *BinarySearchTree {
	// sorting array
	sort.Ints(nums)
	root := buildBinarySearchTree(nums, 0, len(nums)-1)
	return &BinarySearchTree{
		root: root,
	}
}

// GetRoot Get the root node of binary search tree
func (bst *BinarySearchTree) GetRoot() *TreeNode {
	return bst.root
}

// GetMin Get node with the min value
func (bst *BinarySearchTree) GetMin(node *TreeNode) *TreeNode {
	if node == nil {
		return node
	}
	// 循环访问左子结点，直到叶结点时为最小结点，跳出
	for node.Left != nil {
		node = node.Left
	}
	return node
}

// GetInorderNext Get node inorder next
func (bst *BinarySearchTree) GetInorderNext(node *TreeNode) *TreeNode {
	if node == nil || node.Right == nil {
		return node
	}
	node = node.Right
	// 循环访问左子结点，直到叶结点时为最小结点，跳出
	for node.Left != nil {
		node = node.Left
	}
	return node
}

// Search node of binary search tree
func (bst *BinarySearchTree) Search(num int) *TreeNode {
	node := bst.root
	// 循环查找，越过叶结点后跳出
	for node != nil {
		if node.Val < num {
			// 目标结点在 root 的右子树中
			node = node.Right
		} else if node.Val > num {
			// 目标结点在 root 的左子树中
			node = node.Left
		} else {
			// 找到目标结点，跳出循环
			break
		}
	}
	// 返回目标结点
	return node
}

// Insert node of binary search tree
func (bst *BinarySearchTree) Insert(num int) *TreeNode {
	cur := bst.root
	// 若树为空，直接提前返回
	if cur == nil {
		return nil
	}
	// 待插入结点之前的结点位置
	var prev *TreeNode = nil
	// 循环查找，越过叶结点后跳出
	for cur != nil {
		if cur.Val == num {
			return nil
		}
		prev = cur
		if cur.Val < num {
			cur = cur.Right
		} else {
			cur = cur.Left
		}
	}
	// 插入结点
	node := NewTreeNode(num)
	if prev.Val < num {
		prev.Right = node
	} else {
		prev.Left = node
	}
	return cur
}

// Remove node of binary search tree
func (bst *BinarySearchTree) Remove(num int) *TreeNode {
	cur := bst.root
	// 若树为空，直接提前返回
	if cur == nil {
		return nil
	}
	// 待删除结点之前的结点位置
	var prev *TreeNode = nil
	// 循环查找，越过叶结点后跳出
	for cur != nil {
		if cur.Val == num {
			break
		}
		prev = cur
		// 待删除结点在右子树中
		if cur.Val < num {
			cur = cur.Right
		} else {
			// 待删除结点在左子树中
			cur = cur.Left
		}
	}
	// 若无待删除结点，则直接返回
	if cur == nil {
		return nil
	}
	// 子结点数为 0 或 1
	if cur.Left == nil || cur.Right == nil {
		var child *TreeNode = nil
		// 取出待删除结点的子结点
		if cur.Left != nil {
			child = cur.Left
		} else {
			child = cur.Right
		}
		// 将子结点替换为待删除结点
		if prev.Left == cur {
			prev.Left = child
		} else {
			prev.Right = child
		}

	} else { // 子结点数为 2
		// 获取中序遍历中待删除结点 cur 的下一个结点
		next := bst.GetInorderNext(cur)
		temp := next.Val
		// 递归删除结点 next
		bst.Remove(next.Val)
		// 将 next 的值复制给 cur
		cur.Val = temp
	}
	// TODO: add error handler, don't return node
	return cur
}

// buildBinarySearchTree Build a binary search tree from array.
func buildBinarySearchTree(nums []int, left, right int) *TreeNode {
	if left > right {
		return nil
	}
	// 将数组中间结点作为根结点
	middle := left + (right-left)>>1
	root := NewTreeNode(nums[middle])
	// 递归构建左子树和右子树
	root.Left = buildBinarySearchTree(nums, left, middle-1)
	root.Right = buildBinarySearchTree(nums, middle+1, right)
	return root
}

// Print binary search tree
func (bst *BinarySearchTree) Print() {
	PrintTree(bst.root)
}