Arrays & Strings — Chapter Quiz · Data Structures & Algorithms

Question 1

1

What is the time complexity of Array.prototype.shift() in JavaScript?

AO(1)BO(log n)CO(n)DO(n log n)

shift() removes the first element and re-indexes every remaining element, which takes O(n). Use a linked list or a two-pointer approach when you need frequent dequeue from the front.

Question 2

2

The two-pointer technique for finding a pair that sums to a target in a sorted array works because:

AYou can hash both values in O(1)BMoving the left pointer right increases the sum; moving the right pointer left decreases it, so you converge in O(n)CBinary search finds each element in O(log n)DThe array is already hashed by the engine

With a sorted array, two pointers start at opposite ends. If the sum is too small, advance left; if too large, retreat right. Each step eliminates a possibility, giving O(n) overall.

Question 3

3

A sliding window of variable size is typically expanded or shrunk based on:

AA fixed step size defined before the loopBA constraint or condition on the current window contentsCRandom sampling to avoid worst-case inputsDThe length of the input string divided by 2

Variable-width sliding windows grow the right pointer until a constraint is violated, then shrink the left pointer until the window is valid again. This gives amortized O(n).

Question 4

4

Given a prefix-sum array pre where pre[i] = nums[0] + … + nums[i-1], what is the sum of nums[l..r] (inclusive, 0-indexed)?

Apre[r] - pre[l]Bpre[r+1] - pre[l]Cpre[r] + pre[l]Dpre[r+1] + pre[l+1]

With the standard offset definition, the range sum is pre[r+1] - pre[l]. Each query is O(1) after O(n) preprocessing.

Question 5

5

Kadane's algorithm solves which problem in O(n)?

AMaximum subarray sumBLongest increasing subsequenceCSorting an array of 0s, 1s, and 2sDFinding the median in a stream

Kadane's algorithm maintains a running maximum subarray sum, resetting to 0 whenever the running sum goes negative, and tracks the global max. One pass, O(n) time, O(1) space.

Question 6

6

In JavaScript, strings are mutable — you can change individual characters using bracket notation like str[0] = 'X'.

TTrueFFalse

JS strings are immutable primitives. str[0] = 'X' silently fails in non-strict mode. String operations always produce a new string.

Question 7

7

The Dutch National Flag algorithm, invented by Dijkstra, sorts an array of three distinct values using ___ pointers.

The algorithm uses low, mid, and high pointers. Elements before low are the smallest value, between low and mid are the middle value, and after high are the largest. O(n) time, O(1) space.

Question 8

8

Which statements about JavaScript strings and Unicode are correct? (Select all that apply)

Select all that apply.

AJS strings are UTF-16 encoded internallyBEmoji characters often require two UTF-16 code units (a surrogate pair)Cstr.length always equals the number of visible charactersDSpreading a string with [...str] correctly iterates Unicode code points

JS strings are UTF-16. Supplementary code points (like most emoji) need surrogate pairs, so str.length counts code units, not characters. The spread operator uses the string iterator, which correctly yields code points, not code units.

Test what you learned.

Arrays — Chapter Quiz