What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Use a read pointer to scan the sorted list and a write pointer to build the unique prefix in place. Return the write pointer as k: the first k elements hold one copy of each value, in sorted order. The remaining tail is not part of the result and does not need to be removed.
In-place solution for keeping one copy of each value
This implementation follows the contract for LeetCode 26: mutate the input list, keep one occurrence of each value, and return the valid prefix length.
def remove_duplicates(nums):
if not nums:
return 0
write = 1
for read in range(1, len(nums)):
if nums[read] != nums[write - 1]:
nums[write] = nums[read]
write += 1
return writeFor example, given [1, 1, 2, 2, 3], the function returns 3. The first three positions contain [1, 2, 3]; the contents after that prefix can be ignored.
How the read and write pointers work
read scans every input value
The loop starts at index 1 because the first value is already the first unique value. Since the input is sorted in non-decreasing order, duplicates appear next to one another. Each candidate can therefore be compared with the last value retained.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
write marks the next free position
When nums[read] differs from nums[write - 1], it is a new value. The function copies it to nums[write] and advances write. If the values match, it skips the duplicate. At the end, write is the number of unique values and the length of the valid prefix.
Understand the prefix-length contract
The problem specification says, “The first k elements of nums should contain the unique numbers in sorted order.” In other words, k tells the caller how much of the mutated list is valid; the task does not require Python to physically shorten the list.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
If your own code needs an actually shorter list, delete the tail after calling the function:
k = remove_duplicates(nums)
del nums[k:]This resizing is an extra step for callers that need it, not part of the prefix-based return contract.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Edge cases and complexity
- Empty list: returns
0. This is a useful extension for Python callers, although the reference problem specifies nonempty inputs. - One value: returns
1. - All values equal: returns
1. - Already unique: returns the original length.
The scan takes O(n) time and uses O(1) auxiliary space, assuming a mutable list with ordinary indexed access. The input must already be sorted; otherwise, equal values may not be adjacent and this comparison will not remove every duplicate.
Alternative when you want a new list
Python’s itertools.groupby groups consecutive elements with the same key; the Functional Programming HOWTO notes that it assumes input is already grouped or sorted by that key. It can construct a separate list of unique values:
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
from itertools import groupby
unique = [key for key, _ in groupby(nums)]This is concise when preserving the original list matters, but it allocates a new output list rather than rewriting the valid prefix in place.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do not confuse the one-copy task with the at-most-two variation
LeetCode 80 is a related but different problem: it keeps each value at most twice. For that variation, keep an item when fewer than two items have been written, or when it differs from the value two positions behind the write pointer:
Do these 3 things before closing this tab:
1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesBest Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
def keep_at_most_two(nums):
write = 0
for value in nums:
if write < 2 or value != nums[write - 2]:
nums[write] = value
write += 1
return writeUse the first implementation when the requirement is exactly one copy of each value; changing the retention rule changes the answer.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
