104_MaximumDepthofBinaryTree - a920604a/leetcode GitHub Wiki

title: 104. Maximum Depth of Binary Tree

tags:
- backtracking - bfs categories: leetcode comments: false

problem

求二元樹的最大深度

solution

dfs

  • 用遞迴方式，求二元樹的深度，終止條件為當節點不存在時return 0，否則1+max(maxDepth(root->left), maxDepth(root->right)) 
class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root) return 0;
        else return 1+max(maxDepth(root->left), maxDepth(root->right));
    }
};

bfs

  • 用bfs，用queue輔助，儲存拜訪當下節點的左右子節點，並將深度加一
class Solution {
public:
    int maxDepth(TreeNode* root) {
        queue<TreeNode*>q;
        if(!root) return 0;
        int depth = 0;
        q.push(root);
        while(!q.empty()){
            int size = q.size();
            for(int i=0;i<size;++i){
                TreeNode *p = q.front();
                q.pop();
                if(p->left) q.push(p->left);
                if(p->right) q.push(p->right);
            }
            depth++;
        }
        return depth;
    }
};

analysis

  • backtracking time complexity O(n) space complexity O(logN)
  • bfs time complexity O(n) space complexity O(n) , N/2 樹最底層的節點數量

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