题目：

题解：

func largestValues(root *TreeNode) (ans []int) {
    if root == nil {
        return
    }
    q := []*TreeNode{root}
    for len(q) > 0 {
        maxVal := math.MinInt32
        tmp := q
        q = nil
        for _, node := range tmp {
            maxVal = max(maxVal, node.Val)
            if node.Left != nil {
                q = append(q, node.Left)
            }
            if node.Right != nil {
                q = append(q, node.Right)
            }
        }
        ans = append(ans, maxVal)
    }
    return
}

func max(a, b int) int {
    if b > a {
        return b
    }
    return a
}