Talke is cheap.

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

func isBalanced(root *TreeNode) bool {
    return isBalan(root) != -1
}

func isBalan(root *TreeNode) int {
    if root == nil {
        return 0
    }
    left := isBalan(root.Left)
    right := isBalan(root.Right)
    if left == -1 || right == -1 || left - right > 1 || left - right < -1 {
        return -1
    }
    if left > right {
        return left + 1
    }
    return right + 1
}