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.

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與Minimum Depth of Binary Tree對照看

解法一：遞歸，子樹高度+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;elsereturn max(maxDepth(root->left), maxDepth(root->right)) + 1;} };

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解法二：深度優先遍歷，棧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;} };

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