【LeetCode】104. Maximum Depth of Binary Tree (2 solutions)

最新推荐文章于 2025-09-10 15:24:29 发布

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最新推荐文章于 2025-09-10 15:24:29 发布

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文章标签：数据结构与算法

本文介绍了两种方法用于求解二叉树的最大深度：递归方法和深度优先遍历方法。通过实例演示，详细解释了每种方法的实现过程，并对比了它们的优缺点。

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 farthest leaf node.

与Minimum Depth of Binary Tree对照看

解法一：递归，子树高度+1。

/**
 * Definition for binary tree
 * 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 == NULL)
            return 0;
        else
            return max(maxDepth(root->left), maxDepth(root->right)) + 1;
    }
};

解法二：深度优先遍历，栈的最大容量即最大深度

/**
 * Definition for binary tree
 * 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 == NULL)
            return 0;
        stack<TreeNode*> stk;
        unordered_map<TreeNode*, bool> visited;
        stk.push(root);
        int ret = 1;
        visited[root] = true;
        while(!stk.empty())
        {
            TreeNode* top = stk.top();
            if(top->left && visited[top->left] == false)
            {
                stk.push(top->left);
                ret = max(ret, (int)stk.size());
                visited[top->left] = true;
                continue;
            }
            if(top->right && visited[top->right] == false)
            {
                stk.push(top->right);
                ret = max(ret, (int)stk.size());
                visited[top->right] = true;
                continue;
            }
            stk.pop();
        }
        return ret;
    }
};