2583. Kth Largest Sum in a Binary Tree

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problem

solution

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/**
 * 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:
    long long kthLargestLevelSum(TreeNode* root, int k) {
        vector<long long> levels;
        // level traversal
        queue<TreeNode*> q({root});
        while(!q.empty()) {
            int size = q.size();
            long long level = 0;
            for(int i=0;i<size; ++i) {
                TreeNode *node = q.front();
                q.pop();
                level+=node->val;
                if(node->left != nullptr) q.push(node->left);
                if(node->right != nullptr) q.push(node->right);
                // cout<<node->val<<endl;
            }
            levels.push_back(level);
        }
        
        sort(levels.begin(), levels.end(), greater<long long>());
        if( k-1 >= levels.size()) return -1;
        return levels[(k-1)];
        
    }
};

you could replace vector to priority

analysis

  • time complexity O(nlogn)
  • space complexity O(n)