- Postgres – Joins
INNER, LEFT, RIGHT, FULL and CROSS, each with the row count it produces on real tables so the difference is visible rather than described. The LEFT JOIN whose WHERE clause silently turns it back into an INNER JOIN, anti-joins with NOT EXISTS, self-joins, and LATERAL — the one that lets you write top-N-per-group without a window function.
- Max Subset Sum No Adjacent
Write a function that takes in an array of positive integers and returns the maximum sum of non-adjacent elements in the array. If the input array is empty, the function should return 0. Sample input [75, 105, 120, 75, 90, 135] Sample output 330 = 75 + 120 + 135 Solution Time Complexity: O(n) Space…
- Minimal Waiting Time
You’re given a non-empty array of positive integers representing the amounts of time that specific queries take to execute. Only one query can be executed at a time, but the queries can be executed in any order. A query’s waiting time is defined as the amount of time that it must wait before its…
- Nth Fibonacci
The Fibonacci sequence is defined as follows: the first number of the sequence is 0, the second number is 1, and the nth number is the sum of the (n – 1)th and (n – 2)th numbers. Write a function that takes in an integer n and returns the nth Fibonacci number. I have a […]
- Palindrome Check
Write a function that takes in a non-empty string and that returns a boolean representing whether the string is a palindrome. A palindrome is defined as a string that’s written the same forward and backward. Note that single-character strings are palindromes. Solution Loop through half of the…