Find Missing Number (1 to n)
Calculates expected arithmetic sum n*(n+1)//2 and subtracts array sum to reveal the gap.
Live loop — open the studio to scrub, add your own array, or race it in Battle Arena.
Asked in interviews at
Reference implementation (Python)
def find_missing_number(arr):
n = len(arr) + 1
expected_sum = n * (n + 1) // 2
actual_sum = sum(arr)
return expected_sum - actual_sumEmbed this visualization
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<iframe src="/embed/missing-number" 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 Find Missing Number (1 to n)?
Find Missing Number (1 to n) runs in O(n) time and O(1) auxiliary space.
Is the Find Missing Number (1 to n) 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 Find Missing Number (1 to n) in interviews?
Find Missing Number (1 to n) shows up in interviews at Netflix, Amazon, ByteDance.
How does the 3D visualization of Find Missing Number (1 to n) 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.