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[Leetcode]104. Maximum Depth of Binary Tree(C++)

题目描述

题目链接:104. Maximum Depth of Binary Tree

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 nearest leaf node.

例子

Input: [3,9,20,null,null,15,7] Output: 3

Note

  • A leaf is a node with no children.

解题思路

111. Minimum Depth of Binary Tree 可以用 BFS 或者 DFS 求解,代码如下:

方法一: BFS

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        std::queue<TreeNode*> q;
        if (!root) return 0;
        q.push(root);
        int depth = 0;
        while (!q.empty()) {
            depth++;
            std::queue<TreeNode*> next_level;
            while (!q.empty()) {
                TreeNode* node = q.front();
                q.pop();
                if (node->left) next_level.push(node->left);
                if (node->right) next_level.push(node->right);
            }
            std::swap(q, next_level);
        }

        return depth;
    }
};
  • 时间复杂度: O(n)
  • 空间复杂度: O(w)

方法二: DFS

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (!root) return 0;
        int max_depth = 0;
        dfs(root, 0, max_depth);
        
        return max_depth;
    }

private:
    void dfs(TreeNode* node, int current_depth, int& max_depth) {
        if (!node) {
            return;
        }
        current_depth++;
        if (!node->left && !node->right) {
            max_depth = std::max(current_depth, max_depth);
        }

        dfs(node->left, current_depth, max_depth);
        dfs(node->right, current_depth, max_depth);
    }
};
  • 时间复杂度: O(n)
  • 空间复杂度: O(h)

GitHub 代码同步地址: 104.MaximumDepthOfBinaryTree.cpp

其他题目: GitHub: Leetcode-C++-Solution 博客: Leetcode-Solutions

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