【剑指offer】面试题55 - Ⅰ/Ⅱ：二叉树的深度/平衡二叉树

剑指 Offer 55 - I. 二叉树的深度

方法一：

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */
class Solution {
    
public:
    int maxDepth(TreeNode* root) {
    
        if(root == nullptr )
            return 0;
            
        return max( maxDepth(root->left), maxDepth(root->right)) + 1;
    }
    // int maxDepth(TreeNode* root)
    // {
    
    // if( root == nullptr )
    // return 0;
    // int lefHeight = maxDepth(root->left);
    // int rightHeight = maxDepth(root->right);

    // return (lefHeight > rightHeight) ? lefHeight + 1 : rightHeight + 1;
    // }
};

剑指 Offer 55 - II. 平衡二叉树

方法一：递归

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */
class Solution {
    
public:
    bool isBalanced(TreeNode* root) {
    
        if( root == nullptr )
            return true;
        if( abs( Depth(root->left) - Depth(root->right) ) > 1 )
            return false;
        return isBalanced(root->left) && isBalanced(root->right); 
        
    }
    int Depth(TreeNode* root) {
    
        if(root == nullptr )
            return 0;
        return max( Depth(root->left), Depth(root->right)) + 1;
    }
    // int Depth(TreeNode* root)
    // {
    
    // if( root == nullptr )
    // return 0;
    // int lefHeight = Depth(root->left);
    // int rightHeight = Depth(root->right);

    // return (lefHeight > rightHeight) ? lefHeight + 1 : rightHeight + 1;
    // }
};

方法二：