一:题目

二:上码

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public void Order(TreeNode root,HashMap<Integer,Integer>map) {if (root == null) return ;Order(root.left,map);map.put(root.val,map.getOrDefault(root.val,0)+1);Order(root.right,map);}public int[] findMode(TreeNode root) {HashMap<Integer,Integer>map = new HashMap<>();Order(root,map);int maxx = Integer.MIN_VALUE;int count = 0;int count1 = 0;for (Integer key:map.keySet()) {    if (map.get(key) > maxx) {maxx = map.get(key);}}     for (Integer key:map.keySet()) {    if (map.get(key)  == maxx) {count++;}}int[] ans = new int[count];for (Integer key:map.keySet()) {    if (map.get(key)  == maxx) {ans[count1++] = key;}}return ans;}
}