TikTok 2027 CodeSignal OA: Even Digit Count, Cyclic-Shift Difference Sums, Bouncing Diagonals, Most Points in a Range

It felt a bit harder than last year, and the question bank is new. Here are my approaches.

Q1: Does the number have an even number of digits?

Convert it to a string and check whether the length is divisible by 2.

def has_even_digits(x):
    return len(str(abs(x))) % 2 == 0

Q2: Sums of absolute differences after cyclic shifts

Two nested loops: for each shift, compute the sum of absolute differences between aligned positions, collect all the sums, sort them and return. Time O(n²).

def shifted_abs_diff_sums(a, b):
    n = len(a)
    sums = [sum(abs(a[i] - b[(i + s) % n]) for i in range(n)) for s in range(n)]
    return sorted(sums)

Q3: Walk a diagonal, bouncing off walls

Simulate walking along the diagonal and bounce when you hit a wall. Track visited cells in a set so you don't revisit them. Stop at a corner or at an already visited cell, and sum the values along the way.

Q4: Pick a center that covers the most points

Choose a center c and count how many points fall within [c − lim, c + lim]; maximize that count.

It's really asking how many points an interval of length at most 2·lim can cover: sort, then sweep with a sliding window, tracking the maximum count and its center.

def best_center(points, lim):
    """Returns (max number of points, one valid center)"""
    pts = sorted(points)
    best, center, left = 0, None, 0
    for right, x in enumerate(pts):
        while x - pts[left] > 2 * lim:
            left += 1
        if right - left + 1 > best:
            best, center = right - left + 1, pts[left] + lim
    return best, center

Time O(n log n).