Problem: LeetCode June Challenge - Day 25 Ideas Store n in nums[n-1] for each n.

Problem: LeetCode June Challenge - Day 24 Ideas Catalan numbers.

Problem: LeetCode June Challenge - Day 23 Ideas Use a stack instead of recursion for better performance.

Problem: LeetCode June Challenge - Day 22 Solution: class Solution { public: int singleNumber(vector<int>& nums) { unordered_map<int,int> m; for(int x : nums) m[x]++; for(auto pp : m) if(pp.

Problem: LeetCode June Challenge - Day 21 Solution: class Solution { public: int calculateMinimumHP(vector<vector<int>>& dungeon) { if(dungeon.

Problem: LeetCode June Challenge - Day 20 Ideas: It’s easy to get the first digit of the permutation, since there are (n-1)!

Problem: LeetCode June Challenge - Day 19 Ideas: Had to use the hints for this one, but they are all the ideas you need.

Problem: LeetCode June Challenge - Day 18 Ideas: A scientist has h-index k iff he/she has k papers with k citations.

Problem: LeetCode June Challenge - Day 17 Ideas: A region is not surrounded if some element is in the border.

Problem: LeetCode June Challenge - Day 16 Ideas: Use python and regular expressions for an easier life.