https://leetcode.com/problems/most-frequent-subtree-sum/ 4 ms, faster than 95.65%

Leetcode: 508. Most Frequent Subtree Sum

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findFrequentTreeSum(root *TreeNode) []int {
    counts := map[int]int{}
    
    var countSum func(node *TreeNode) int
    countSum = func(node *TreeNode) int {
        if node == nil {
            return 0
        }
        var treeSum = node.Val + countSum(node.Left) + countSum(node.Right)
        counts[treeSum]++
        return treeSum
    }
    countSum(root)
    
    frequentCounts := []int{}
    highestFreq := 0
    for count, freq := range counts {
        if freq > highestFreq {
            frequentCounts = []int{count}
            highestFreq = freq
        } else if freq == highestFreq {
            frequentCounts = append(frequentCounts, count)
        }
    }
    return frequentCounts
}