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// @Title: 平衡二叉树 (Balanced Binary Tree)
// @Author: 15816537946@163.com
// @Date: 2020-06-25 07:15:36
// @Runtime: 8 ms
// @Memory: 5.7 MB
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isBalanced(root *TreeNode) bool {
	_, isBalanced := recur(root)
	return isBalanced
}

func recur(root *TreeNode) (int, bool) {
	if root == nil {
		return 0, true
	}

	lt, lBalanced := recur(root.Left)
	rt, rBalanced := recur(root.Right)

	if lBalanced && rBalanced &&
		-1 <= lt-rt && lt-rt <= 1 {
		return 1 + max(lt, rt), true
	}
	return 0, false
}

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