104. Maximum Depth of Binary Tree

题目

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

解析

// Maximum Depth of Binary Tree
class Solution {
public:

    // Time Limit Exceeded
    int maxDepth1(TreeNode *root) {

        if (!root)
        {
            return  0;
        }

        return (maxDepth(root->left) > maxDepth(root->right)) ? (maxDepth(root->left) + 1) : (maxDepth(root->right)+1);
    }

    // 这样写不会超时
    int maxDepth(TreeNode* root) {
        if (root == NULL) 
            return 0;
        return max(maxDepth(root->left), maxDepth(root->right)) + 1;
    }
    int maxDepth(TreeNode *root)
    {
        if (!root)
        {
            return 0;
        }
        queue<TreeNode*> que;
        que.push(root);

        int level = 0;
        while (!que.empty())
        {
            int size = que.size();
            for (int i = 0; i < size;i++)
            {
                TreeNode* temp = que.front();
                que.pop();

                if (temp->left)
                {
                    que.push(temp->left);
                }
                if (temp->right)
                {
                    que.push(temp->right);
                }
            }
            level++;
        }

        return level;
    }
};

104. Maximum Depth of Binary Tree