2021-08-05：监控二叉树。给定一个二叉树，我们在树的节点上安装摄像头。节点上的每个摄影头都可以监视其父对象、自身及其直接

package main

import "fmt"

func main() {
    root := &TreeNode{value: 1}
    root.left = &TreeNode{value: 2}
    root.right = &TreeNode{value: 3}
    root.left.left = &TreeNode{value: 4}
    ret := minCameraCover2(root)
    fmt.Println(ret)
}

func minCameraCover2(root *TreeNode) int {
    data := process2(root)
    return data.cameras + twoSelectOne(data.status == UNCOVERED, 1, 0)
}

func twoSelectOne(c bool, a int, b int) int {
    if c {
        return a
    } else {
        return b
    }
}

type TreeNode struct {
    value int
    left  *TreeNode
    right *TreeNode
}
type Status int

const UNCOVERED = 0
const COVERED_NO_CAMERA = 1
const COVERED_HAS_CAMERA = 2

// 以x为头，x下方的节点都是被covered，得到的最优解中：
// x是什么状态，在这种状态下，需要至少几个相机
type Data struct {
    status  Status
    cameras int
}

func process2(X *TreeNode) *Data {
    if X == nil {
        return &Data{COVERED_NO_CAMERA, 0}
    }
    left := process2(X.left)
    right := process2(X.right)
    cameras := left.cameras + right.cameras

    // 左、或右，哪怕有一个没覆盖
    if left.status == UNCOVERED || right.status == UNCOVERED {
        return &Data{COVERED_HAS_CAMERA, cameras + 1}
    }

    // 左右孩子，不存在没被覆盖的情况
    if left.status == COVERED_HAS_CAMERA || right.status == COVERED_HAS_CAMERA {
        return &Data{COVERED_NO_CAMERA, cameras}
    }
    // 左右孩子，不存在没被覆盖的情况，也都没有相机
    return &Data{UNCOVERED, cameras}
}