leetcode-go/medium/508.most-frequent-subtree-sum.go

var max int = 0

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findFrequentTreeSum(root *TreeNode) (res []int) {
	max = 0
	freq := make(map[int]int)
	postorder(root, &freq)
	for k, v := range freq {
		if v == max {
			res = append(res, k)
		}
	}
	return
}

func postorder(root *TreeNode, freq *map[int]int) int {
	if root == nil {
		return 0
	}
	l := postorder(root.Left, freq)
	r := postorder(root.Right, freq)
	sum := l + r + root.Val
	(*freq)[sum]++
	if max < (*freq)[sum] {
		max = (*freq)[sum]
	}
	return sum
}