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package Tree;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.LinkedList;

import java.util.List;

/**

* 题目要求不使用额外空间，找到树中出现频率最多的结点，如果有多个，输出多个

* 不使用额外空间，利用两次中序遍历

*/

public class FindModeinBinarySearchTree_501 {

//次数

private int modeTimes;

//最大次数

private int maxModeTimes;

//上一个结点的值

private int lastValue;

public int[] findMode(TreeNode root) {

if(root==null) return new int[]{};

modeTimes=0;

maxModeTimes=0;

lastValue=root.val;

findMaxFre(root);

List<Integer> list = new ArrayList<>();

//对变量进行还原，以便进行第二次中序遍历

lastValue=root.val;

modeTimes=0;

inorder(root, list);

int[] result=new int[list.size()];

for(int i=0;i<result.length;i++){

result[i]=list.get(i);

}

return result;

}

//第一次中序遍历，找到最大频数

private void findMaxFre(TreeNode root) {

if (root != null) {

findMaxFre(root.left);

if(root.val==lastValue){

modeTimes ++;

}else{

modeTimes=1;

lastValue=root.val;

}

maxModeTimes=Math.max(maxModeTimes,modeTimes);

findMaxFre(root.right);

}

}

private void inorder (TreeNode root,List<Integer> list){

if (root != null) {

inorder(root.left,list);

if(root.val==lastValue){

modeTimes++;

}else{

modeTimes=1;

lastValue=root.val;

}

//找到次数等于最大次数的值，将其加入到链表中

if(modeTimes==maxModeTimes){

list.add(root.val);

}

inorder(root.right,list);

}

}

/**

* 以下利用中序遍历和HashMap，HashMap中存储值与它的频数

*/

private HashMap<Integer, Integer> map;

private Integer max = 0;

private int count = 0;

public int[] findMode1 (TreeNode root){

map = new HashMap<>();

inorder1(root);

int[] result = new int[count];

int j = 0;

for (int i : map.keySet()) {

if (map.get(i).equals(max)) {

result[j++] = i;

}

}

return result;

}

private void inorder1 (TreeNode root){

if (root != null) {

inorder1(root.left);

int fre = map.getOrDefault(root.val, 0) + 1;

if (fre == max) {

count++;

}

if (fre > max) {

max = fre;

count = 1;

}

map.put(root.val, fre);

inorder1(root.right);

}

}

}