LeetCode 104. 二叉树的最大深度(二叉树基础之——二叉树的深度)

DFS:

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root) return 0;
        return 1+max(maxDepth(root->left),maxDepth(root->right));   
    }
};

BFS：

/**
 * 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) {
        int layer = 0;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int size = q.size();
            while(size--){
                TreeNode* r = q.front();
                q.pop();
                if(!r){
                    continue;
                }
                q.push(r->left);
                q.push(r->right);
            }
            layer++;
        }
        return layer-1;
    }
};