// File: preorder_traversal_i_compact.go
// Created Time: 2023-05-09
// Author: Reanon (793584285@qq.com)

package chapter_backtracking

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

/* 判断当前状态是否为解 */
func isSolution(state *[]*TreeNode) bool {
	return len(*state) != 0 && (*state)[len(*state)-1].Val == 7
}

/* 记录解 */
func recordSolution(state *[]*TreeNode, res *[][]*TreeNode) {
	*res = append(*res, *state)
}

/* 判断在当前状态下，该选择是否合法 */
func isValid(state *[]*TreeNode, choice *TreeNode) bool {
	return choice != nil && choice.Val != 3
}

/* 更新状态 */
func makeChoice(state *[]*TreeNode, choice *TreeNode) {
	*state = append(*state, choice)
}

/* 恢复状态 */
func undoChoice(state *[]*TreeNode, choice *TreeNode) {
	*state = (*state)[:len(*state)-1]
}

/* 回溯算法：例题三 */
func backtrackIII(state *[]*TreeNode, choices *[]*TreeNode, res *[][]*TreeNode) {
	// 检查是否为解
	if isSolution(state) {
		// 记录解
		recordSolution(state, res)
		return
	}
	// 遍历所有选择
	for _, choice := range *choices {
		// 剪枝：检查选择是否合法
		if isValid(state, choice) {
			// 尝试：做出选择，更新状态
			makeChoice(state, choice)
			// 进行下一轮选择
			temp := make([]*TreeNode, 0)
			temp = append(temp, choice.Left, choice.Right)
			backtrackIII(state, &temp, res)
			// 回退：撤销选择，恢复到之前的状态
			undoChoice(state, choice)
		}
	}
}
