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package class07;
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// 本题测试链接 : https://leetcode.com/problems/binary-tree-cameras/
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public class Code02_MinCameraCover {
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public static class TreeNode {
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public int value;
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public TreeNode left;
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public TreeNode right;
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}
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public static int minCameraCover1(TreeNode root) {
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Info data = process1(root);
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return (int) Math.min(data.uncovered + 1, Math.min(data.coveredNoCamera, data.coveredHasCamera));
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}
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// 潜台词：x是头节点，x下方的点都被覆盖的情况下
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public static class Info {
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public long uncovered; // x没有被覆盖，x为头的树至少需要几个相机
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public long coveredNoCamera; // x被相机覆盖，但是x没相机，x为头的树至少需要几个相机
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public long coveredHasCamera; // x被相机覆盖了，并且x上放了相机，x为头的树至少需要几个相机
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public Info(long un, long no, long has) {
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uncovered = un;
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coveredNoCamera = no;
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coveredHasCamera = has;
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}
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}
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// 所有可能性都穷尽了
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public static Info process1(TreeNode X) {
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if (X == null) { // base case
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return new Info(Integer.MAX_VALUE, 0, Integer.MAX_VALUE);
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}
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Info left = process1(X.left);
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Info right = process1(X.right);
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// x uncovered x自己不被覆盖，x下方所有节点，都被覆盖
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// 左孩子： 左孩子没被覆盖，左孩子以下的点都被覆盖
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// 左孩子被覆盖但没相机，左孩子以下的点都被覆盖
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// 左孩子被覆盖也有相机，左孩子以下的点都被覆盖
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long uncovered = left.coveredNoCamera + right.coveredNoCamera;
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// x下方的点都被covered，x也被cover，但x上没相机
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long coveredNoCamera = Math.min(
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// 1)
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left.coveredHasCamera + right.coveredHasCamera,
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Math.min(
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// 2)
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left.coveredHasCamera + right.coveredNoCamera,
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// 3)
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left.coveredNoCamera + right.coveredHasCamera));
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// x下方的点都被covered，x也被cover，且x上有相机
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long coveredHasCamera =
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Math.min(left.uncovered, Math.min(left.coveredNoCamera, left.coveredHasCamera))
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+ Math.min(right.uncovered, Math.min(right.coveredNoCamera, right.coveredHasCamera))
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+ 1;
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return new Info(uncovered, coveredNoCamera, coveredHasCamera);
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}
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public static int minCameraCover2(TreeNode root) {
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Data data = process2(root);
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return data.cameras + (data.status == Status.UNCOVERED ? 1 : 0);
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}
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// 以x为头，x下方的节点都是被covered，x自己的状况，分三种
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public static enum Status {
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UNCOVERED, COVERED_NO_CAMERA, COVERED_HAS_CAMERA
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}
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// 以x为头，x下方的节点都是被covered，得到的最优解中：
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// x是什么状态，在这种状态下，需要至少几个相机
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public static class Data {
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public Status status;
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public int cameras;
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public Data(Status status, int cameras) {
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this.status = status;
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this.cameras = cameras;
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}
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}
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public static Data process2(TreeNode X) {
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if (X == null) {
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return new Data(Status.COVERED_NO_CAMERA, 0);
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}
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Data left = process2(X.left);
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Data right = process2(X.right);
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int cameras = left.cameras + right.cameras;
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// 左、或右，哪怕有一个没覆盖
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if (left.status == Status.UNCOVERED || right.status == Status.UNCOVERED) {
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return new Data(Status.COVERED_HAS_CAMERA, cameras + 1);
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}
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// 左右孩子，不存在没被覆盖的情况
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if (left.status == Status.COVERED_HAS_CAMERA || right.status == Status.COVERED_HAS_CAMERA) {
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return new Data(Status.COVERED_NO_CAMERA, cameras);
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}
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// 左右孩子，不存在没被覆盖的情况，也都没有相机
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return new Data(Status.UNCOVERED, cameras);
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}
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}
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