【题目2】
给定一颗二叉树的头结点head，任何两个结点之间都存在距离，返回整颗二叉树的最大距离
package com.harrison.class08;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
public class Code02_MaxDistance {
public static class Node {
public int value;
public Node left;
public Node right;
public Node(int data) {
this.value = data;
}
}
public static class Info {
public int maxDistance;
public int height;
public Info(int m, int h) {
maxDistance = m;
height = h;
}
}
public static int maxDistance1(Node head) {
return process1(head).maxDistance;
}
public static Info process1(Node head) {
if (head == null) {
return new Info(0, 0);
}
Info leftInfo = process1(head.left);
Info rightInfo = process1(head.right);
int height = Math.max(leftInfo.height, rightInfo.height) + 1;
int maxDistance = Math.max(
Math.max(leftInfo.maxDistance, rightInfo.maxDistance),
leftInfo.height + rightInfo.height + 1);
return new Info(maxDistance, height);
}
public static int maxDistance2(Node head) {
if (head == null) {
return 0;
}
ArrayList<Node> arr = getPrelist(head);
HashMap<Node, Node> parentMap = getParentMap(head);
int max = 0;
for (int i = 0; i < arr.size(); i++) {
for (int j = i; j < arr.size(); j++) {
max = Math.max(max, distance(parentMap, arr.get(i), arr.get(j)));
}
}
return max;
}
public static ArrayList<Node> getPrelist(Node head) {
ArrayList<Node> arr = new ArrayList<>();
fillPrelist(head, arr);
return arr;
}
public static void fillPrelist(Node head, ArrayList<Node> arr) {
if (head == null) {
return;
}
arr.add(head);
fillPrelist(head.left, arr);
fillPrelist(head.right, arr);
}
public static HashMap<Node, Node> getParentMap(Node head) {
HashMap<Node, Node> map = new HashMap<>();
map.put(head, null);
fillParentMap(head, map);
return map;
}
public static void fillParentMap(Node head, HashMap<Node, Node> parentMap) {
if (head.left != null) {
parentMap.put(head.left, head);
fillParentMap(head.left, parentMap);
}
if (head.right != null) {
parentMap.put(head.right, head);
fillParentMap(head.right, parentMap);
}
}
public static int distance(HashMap<Node, Node> parentMap, Node o1, Node o2) {
HashSet<Node> o1Set = new HashSet<>();
Node cur = o1;
o1Set.add(cur);
while (parentMap.get(cur) != null) {
cur = parentMap.get(cur);
o1Set.add(cur);
}
cur = o2;
while (!o1Set.contains(cur)) {
cur = parentMap.get(cur);
}
Node lowestAncestor = cur;
cur = o1;
int distance1 = 1;
while (cur != lowestAncestor) {
cur = parentMap.get(cur);
distance1++;
}
cur = o2;
int distance2 = 1;
while (cur != lowestAncestor) {
cur = parentMap.get(cur);
distance2++;
}
return distance1 + distance2 - 1;
}
public static Node generateRandomBST(int maxLevel, int maxValue) {
return generate(1, maxLevel, maxValue);
}
public static Node generate(int level, int maxLevel, int maxValue) {
if (level > maxLevel || Math.random() < 0.5) {
return null;
}
Node head = new Node((int) (Math.random() * maxValue));
head.left = generate(level + 1, maxLevel, maxValue);
head.right = generate(level + 1, maxLevel, maxValue);
return head;
}
public static void main(String[] args) {
int maxLevel = 4;
int maxValue = 100;
int testTimes = 1000000;
for (int i = 0; i < testTimes; i++) {
Node head = generateRandomBST(maxLevel, maxValue);
if (maxDistance1(head) != maxDistance2(head)) {
System.out.println("Oops!");
}
}
System.out.println("finish!");
}
}