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HashEasyLeetCode #387

First Unique Element (Hash Map)

Identifies the first non-repeating element using two-pass hash map count in O(n) time.

Time O(n) Space O(n)
Open in 3D Studio

Live loop — open the studio to scrub, add your own array, or race it in Battle Arena.

Asked in interviews at

AmazonBloombergGoogle

Reference implementation (Python)

def first_unique(arr):
    counts = {}
    for x in arr:
        counts[x] = counts.get(x, 0) + 1
    for i, x in enumerate(arr):
        if counts[x] == 1:
            return i
    return -1

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Drop a live, looping First Unique Element (Hash Map) canvas into a blog post or course page.

<iframe src="/embed/first-unique-char" 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 First Unique Element (Hash Map)?

First Unique Element (Hash Map) runs in O(n) time and O(n) auxiliary space.

Is the First Unique Element (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 First Unique Element (Hash Map) in interviews?

First Unique Element (Hash Map) shows up in interviews at Amazon, Bloomberg, Google.

How does the 3D visualization of First Unique Element (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.

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