501. 二叉搜索树中的众数

输入：root = [1,null,2,2]
输出：[2]

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findMode(root *TreeNode) []int {
    r := map[int]int{}
    search(root, r)

    max := -1
    res := []int{}
    for n, v := range r {
        if max <= v {
            if max < v {
                max = v
                res = res[0:0]
            }
            res = append(res, n)
        }
    }

    return res
}

func search(root *TreeNode, rec map[int]int) {
    if root == nil {
        return
    }

    rec[root.Val]++

    search(root.Left, rec)
    search(root.Right, rec)
}