Solution.go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func tree2str(root *TreeNode) string {
	if root == nil {
		return ""
	}
	if root.Left == nil && root.Right == nil {
		return strconv.Itoa(root.Val)
	}
	if root.Right == nil {
		return strconv.Itoa(root.Val) + "(" + tree2str(root.Left) + ")"
	}
	return strconv.Itoa(root.Val) + "(" + tree2str(root.Left) + ")(" + tree2str(root.Right) + ")"
}