Hashing
Date: March 23, 2026 • Time: 5:00 PM • Location: Online (Jitsi)
Meeting Notes
we went over three problems from Neetcode:
Everyone did a great job presenting!
For next week
We’re going to continue the topic of Hash maps and also go into Two-pointers. For now, we’ll continue trying this format of presenting with the intention of getting better at explaining concepts and solutions, which is really helpful for interviews!
More Hashing Problems
- 1832. Check if the Sentence Is Pangram
- 268. Missing Number
- 1426. Counting Elements (P)
- 2225. Find Players With Zero or One Losses
- 1133. Largest Unique Number
- 1189. Maximum Number of Balloons
1832. Check if the Sentence Is Pangram
A pangram is a sentence where every letter of the English alphabet appears at least once.
Given a string sentence containing only lowercase English letters, return true if sentence is a pangram, or false otherwise.
Example 1:
Input: sentence = "thequickbrownfoxjumpsoverthelazydog"Output: trueExplanation: sentence contains at least one of every letter of the English alphabet.Example 2:
Input: sentence = "leetcode"Output: false268.Missing Number
Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.
Example 1:
Input: nums = [3,0,1]
Output: 2Explanation:
n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.
Example 2:
Input: nums = [0,1]
Output: 2Explanation:
n = 2 since there are 2 numbers, so all numbers are in the range [0,2]. 2 is the missing number in the range since it does not appear in nums.
Example 3:
Input: nums = [9,6,4,2,3,5,7,0,1]
Output: 8Explanation:
n = 9 since there are 9 numbers, so all numbers are in the range [0,9]. 8 is the missing number in the range since it does not appear in nums.
Constraints:
n == nums.length1 <= n <= 1040 <= nums[i] <= nAll the numbers of nums are unique.Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
1426. Counting Elements
Given an integer array arr, count how many elements x there are, such that x + 1 is also in arr. If there are duplicates in arr, count them separately.
Example 1:
Input: arr = [1,2,3]Output: 2Explanation: 1 and 2 are counted cause 2 and 3 are in arr.Example 2:
Input: arr = [1,1,3,3,5,5,7,7]Output: 0Explanation: No numbers are counted, cause there is no 2, 4, 6, or 8 in arr.Constraints:
1 <= arr.length <= 10000 <= arr[i] <= 1000Given an integer array arr, count how many elements x there are, such that x + 1 is also in arr. If there are duplicates in arr, count them separately.
Example 1:
Input: arr = [1,2,3] Output: 2 Explanation: 1 and 2 are counted cause 2 and 3 are in arr.
Example 2:
Input: arr = [1,1,3,3,5,5,7,7] Output: 0 Explanation: No numbers are counted, cause there is no 2, 4, 6, or 8 in arr.
Constraints:
1 <= arr.length <= 10000 <= arr[i] <= 1000