leetcode-----104. 二叉树的最大深度

• https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/

算法1（dfs）

代码

/**
 * 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) {
        return dfs(root);
    }

    int dfs(TreeNode* root) {
        if (!root) return 0;
        if (!root->left && !root->right) return 1;
        return max(dfs(root->left), dfs(root->right)) + 1;
    }
};

算法2（bfs）

代码

/**
 * 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) {
        queue<TreeNode*> q;
        if (!root) return 0;
        if (!root->left && !root->right) return 1;
        q.push(root);
        int ans = 0;
        while (!q.empty()) {
            ans += 1;
            int sz = q.size();
            for (int i = 0; i < sz; ++i) {
                auto t = q.front();
                q.pop();
                if (t->left) {
                    q.push(t->left);
                }
                if (t->right) {
                    q.push(t->right);
                }
            }
        }
        return ans;
    }
};