TikTok / ByteDance OA All 4 Questions AC Debrief

Just finished a ByteDance OA this morning — same CodeSignal platform as TikTok. 70 minutes, 4 questions, solved in ~15 minutes. All questions are drawn from a question bank. Here's the full breakdown.

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Exam Overview

Item	Details
Platform	CodeSignal
Duration	70 minutes
Questions	4
Difficulty	Easy ~ Medium
Role	Intern / New Grad SDE
Result	All AC, ~15 minutes

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T1: Interval Lookup

Problem Summary

Given an initial value and an array, compute initial + sum(array), determine which interval it falls into, and return the corresponding label string.

Solution

def interval_lookup(initial: int, arr: list, intervals: list, labels: list) -> str:
    total = initial + sum(arr)
    for i, (lo, hi) in enumerate(intervals):
        if lo <= total < hi:
            return labels[i]
    return labels[-1]

# Example
print(interval_lookup(5, [3,2,1], [(0,5),(5,10),(10,20)], ["low","mid","high"]))
# total=11 → "high"

Time: O(n + k) | Space: O(1)

Key points:

• Watch open/closed boundaries (< vs <=)
• For large k use binary search: O(n + log k)

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T2: Vowel Word Flip

Problem Summary

For each word where both first and last characters are vowels, reverse the middle characters, keeping first and last unchanged.

Solution

def vowel_word_flip(words: list) -> list:
    vowels = set('aeiouAEIOU')
    result = []
    for word in words:
        if len(word) >= 2 and word[0] in vowels and word[-1] in vowels:
            result.append(word[0] + word[1:-1][::-1] + word[-1])
        else:
            result.append(word)
    return result

# Example
print(vowel_word_flip(["abcde", "hello"]))
# abcde → a + "bcd"[::-1] + e = "adcbe"

Time: O(n·m) | Space: O(n·m)

Key points:

• Guard len >= 2 for single-char words
• Python slice [::-1] reverses in one line

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T3: Battery Scheduler

Problem Summary

Use phone for t minutes with n batteries of varying capacity and charge rate. Rotate batteries — when one dies, switch to a charged one. Find the minimum number of fully-charged batteries needed.

Solution

import heapq

def min_batteries(t: int, capacity: list, charge_rate: list) -> int:
    n = len(capacity)
    ready = [(0, i) for i in range(n)]
    heapq.heapify(ready)
    charging = []
    current_time = 0
    batteries_used = 0

    while current_time < t:
        while charging and charging[0][0] <= current_time:
            heapq.heappush(ready, heapq.heappop(charging))
        if not ready:
            return -1
        _, idx = heapq.heappop(ready)
        batteries_used += 1
        use_until = current_time + capacity[idx]
        if use_until >= t:
            return batteries_used
        charge_time = use_until + capacity[idx] / charge_rate[idx]
        heapq.heappush(charging, (charge_time, idx))
        current_time = use_until

    return batteries_used

Time: O(k log n) | Space: O(n)

Key points:

• min-heap tracks earliest available charged battery
• charge_time = use_until + capacity / charge_rate
• If use_until >= t, current battery covers the rest

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T4: Chain Traversal

Problem Summary

Given a chain (linear graph), output the traversal order starting from either endpoint.

Solution

from collections import defaultdict

def chain_traversal(n: int, edges: list) -> list:
    adj = defaultdict(list)
    for u, v in edges:
        adj[u].append(v)
        adj[v].append(u)

    start = next((node for node in range(1, n+1) if len(adj[node]) == 1), 1)
    path, prev, curr = [start], None, start

    while True:
        nxt = next((nb for nb in adj[curr] if nb != prev), None)
        if nxt is None:
            break
        path.append(nxt)
        prev, curr = curr, nxt

    return path

print(chain_traversal(5, [(1,2),(2,3),(3,4),(4,5)]))
# [1, 2, 3, 4, 5]

Time: O(n) | Space: O(n)

Key points:

• Endpoint = degree-1 node
• Track only prev, no full visited set needed on a chain
• No BFS/DFS — plain while-loop simulation

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Complexity Summary

Question	Algorithm	Time	Space
T1 Interval Lookup	if-else	O(n+k)	O(1)
T2 Vowel Flip	set + slice	O(n·m)	O(n·m)
T3 Battery Scheduler	Greedy + heap	O(k log n)	O(n)
T4 Chain Traversal	Adj list + while	O(n)	O(n)

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Common Mistakes

Q	Pitfall	Fix
T1	Open/closed boundary confusion	Read carefully, use < vs <=
T2	Single-char word edge case	Guard len >= 2
T3	Mixed time units for charge	Unify to minutes: use_until + cap/rate
T4	Full visited set causes issues	On a chain, just track prev

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CodeSignal OA Strategy

TikTok / ByteDance OA Profile

• Platform: CodeSignal (same as Meta)
• Duration: 70 min, 4 questions
• Source: Random draws from a question bank — high repeat rate
• Difficulty: Easy~Medium, no Hard DP or complex graph theory
• Scoring: Partial credit per test case

Exam Day Tips

1. Scan all 4 questions first — start with the easiest
2. T1/T2 should take under 5 min each — secure full marks first
3. T3/T4 need simulation — watch edge cases, budget 20 min
4. Run provided examples before submitting
5. Review edge cases if time allows: empty arrays, single node, t=0

Related LeetCode Problems

#	Problem	Relevant To
1893	Check if Range is Covered	T1
557	Reverse Words in a String III	T2
1642	Furthest Building You Can Reach	T3
1971	Find if Path Exists in Graph	T4

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