Arrays

Question 1

Two Number Sum

Answer 1

O(nlog(n) time | O(1) Space
Use two pointers starting at opposite ends of a sorted array. Move inward in steps until pointers are equal or a matching pair is found.

Question 2

Validate Subsequence

Answer 2

O(n) time | O(1) space
Use a pointer starting at index 0 of sequence. Iterate over array and compare against value at pointer. If value is next in sequence increment pointer. If all values are found in sequence return true

Question 3

Sorted Squared Array

Answer 3

O(n) time | O(n) space
Use 2 pointers at opposite ends of array. Get absolute value of values under pointers. Prepend the larger value and move pointer inward. Loop n number of times where n is length of input array.