头脑风暴：二叉搜索树中的众数

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/** * 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 {    private List<Integer> list;    public int[] findMode(TreeNode root) {        list = new ArrayList();        inOrder(root);
        Map<Integer, Integer> map = new HashMap();        int maxLen = Integer.MIN_VALUE;        // 扫描有序数组，求得最高频率        for (int value :list) {            map.put(value, map.getOrDefault(value, 0) + 1);            if (maxLen < map.get(value)) {                maxLen = map.get(value);            }         }
        if (maxLen > 0) {            // 遍历哈希表，得出出现频率最高的值            List<Integer> ans = new ArrayList<>();            for (int b:map.keySet()) {                if (map.get(b).equals(maxLen)) {                    ans.add(b);                }            }            int answ[] = new int[ans.size()];            for (int i = 0; i < ans.size(); i++) {                answ[i] = ans.get(i);            }            return answ;        }
        return new int[0];    }        // 中序遍历    public void inOrder(TreeNode node){        if (node == null) return;        inOrder(node.left);        list.add(node.val);        inOrder(node.right);    }}