leetcode 110 balanced binary tree

Whether it is balanced binary tree?

Title:
Given a binary tree to determine whether it is a highly balanced binary tree.
In this problem, a well-balanced binary tree is defined as:
the absolute value of the difference between the height of the left and right subtrees a binary tree each node is not more than 1.

Examples:
Example 1:
a given binary tree [3,9,20, null, null, 15,7 ]

    3
   / \
  9  20
    /  \
   15   7

Return true.
Example 2:
given binary tree [1,2,2,3,3, null, null, 4,4 ]

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

Topic analysis

• Target: each node of the height difference of the left and right subtrees absolute value if less than or equal to 1

1. Looking left and right sub-tree of depth can ⇒ recursive
2. Left subtree is determined whether the difference in depth not more than 1

Ideas analysis

variable	effect
depth()	Solving the left and right sub-tree depth

Suppose the depth of the bottom layer up to the 0 +1
depth ⇒ left and right subtrees of the node to a depth greater value plus 1

process

1. If the current node's left and right subtrees height difference is greater than 1 ⇒ return false
2. Determining whether or not the left and right subtrees balanced binary tree recursive ⇒

code show as below

 int depth(TreeNode*root)
 {
     if(!root) return 0;
     return 1 + max(depth(root->left),depth(root->right));
 }
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        if(abs(depth(root->left)-depth(root->right))>1) return false;
        return isBalanced(root->left)&&isBalanced(root->right);
    }   
};