Two Sum (Hash Map)
Finds two indices whose sum matches target in O(n) single pass using hash lookups.
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Asked in interviews at
Reference implementation (Python)
def two_sum(nums, target):
seen = {}
for i, num in enumerate(nums):
comp = target - num
if comp in seen:
return [seen[comp], i]
seen[num] = i
return []Embed this visualization
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<iframe src="/embed/two-sum-hash" width="100%" height="380" style="border:1px solid #e6e8ec;border-radius:14px" loading="lazy" title="3D algorithm visualization by CodeWithMunnaX"></iframe>Frequently asked
What is the time and space complexity of Two Sum (Hash Map)?
Two Sum (Hash Map) runs in O(n) time and O(n) auxiliary space.
Is the Two Sum (Hash Map) visualizer free?
The core 3D visualizer, Web Audio chimes and step intuition are free. A one-time ₹49 Pro Pass unlocks advanced algorithms, large custom arrays, Battle Arena and reel export.
Which companies ask Two Sum (Hash Map) in interviews?
Two Sum (Hash Map) shows up in interviews at Google, Amazon, Meta, Microsoft, Apple.
How does the 3D visualization of Two Sum (Hash Map) work?
Each array value becomes a 3D pillar whose height maps to its value. Comparisons glow amber, swaps flash red, and settled elements lock green while a floating pointer badge tracks the active index — synchronized line-by-line with the Python code.