剑指54二叉搜索树的第K大结点 55 二叉树的深度

class Solution {
public:
    int kthLargest(TreeNode* root, int k) {
        dfs(root);
        sort(result.begin(),result.end());
        reverse(result.begin(),result.end());
        if(k>=result.size()) return result[result.size()-1];
        return result[k-1];
    }
private:
   vector<int> result;
   void dfs(TreeNode* root)
   {
       if(!root) return ;
       result.push_back(root->val);
       dfs(root->left);
       dfs(root->right);
   }
};

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root) return 0;
        dfs(root,0);//从0开始计数
        return depth;
    }
private:
    int depth=1;
    void dfs(TreeNode* root,int dep)
    {
        if(!root) 
        {
         depth=max(depth,dep);
         return ;
        }
        dep++;
        dfs(root->left,dep);//dfs前面会对每个进来的结点判空 空就return 所以这边不要判空
        dfs(root->right,dep);
    }
};

采用迭代 队列写写看

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root) return 0;//不要忘记好吧求求你了
        int depth=0;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty())
        {
            int size=q.size();
            while(size--)
            {
                TreeNode* t=q.front();
                q.pop();
                if(t->left) q.push(t->left);
                if(t->right) q.push(t->right);          
            }
            depth++;
        }
        return depth;
    }
};