Today I have done Count Complete Tree Nodes on leetcode and leetcode's November LeetCoding Challenge with cpp.

Count Complete Tree Nodes

Description

Given a complete binary tree, count the number of nodes.

Note:

Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

Example:

Input: 
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

Solution

nothing to say

/**
 * 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:
    int countNodes(TreeNode* root) {
        if(!root) return 0;
        return 1+countNodes(root->left)+countNodes(root->right);
    }
};

November LeetCoding Challenge 18

Description

Merge Intervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Example 1

Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

Input: intervals = [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.

Constraints:

• 1 <= intervals.length <= 104
• intervals[i].length == 2
• 0 <= starti <= endi <= 104

Solution

nothing to say

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<pair<int, int>> q;
        for(auto &interval : intervals) {
            q.push_back(make_pair(interval[0], 0));
            q.push_back(make_pair(interval[1], 1));
        }
        sort(q.begin(), q.end());
        
        vector<vector<int>> answer;
        int cnt = 0;
        int start = -1;
        for(auto &[point, type] : q) {
            if(type == 1) {
                cnt -= 1;
                if(cnt == 0) {
                    answer.push_back({start, point});
                }
            }
            if(type == 0) {
                if(cnt == 0) {
                    start = point;
                }
                cnt += 1;
            }
        }
        return answer;
    }
};