Two Pointers/Sort ColorsMedium

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Sort Colors

Two Pointers·Medium

Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white, and blue.

We will use the integers 0, 1, and 2 to represent red, white, and blue, respectively.

You must solve this problem without using the library's sort function, in a single pass and constant extra space (the Dutch National Flag algorithm). For test convenience the function should return the mutated array.

Examples

Input: nums = [2,0,2,1,1,0]

Output: [0,0,1,1,2,2]

Input: nums = [2,0,1]

Output: [0,1,2]

Input: nums = [0]

Output: [0]

Constraints

n == nums.length
1 <= n <= 300
nums[i] is either 0, 1, or 2.

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Tests

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Passed32 ms

First attempt — retry to track metric movement here.

Your approach

Pattern:Two Pointers
Time:O(N)
Space:O(1)

Complete approach — pattern and complexity both named.

Coach

What you got right

You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.

Where it diverged

No divergence detected. The code correctly aligns with the stated approach.

Next attempt: focus on

Try solving related sliding window problems to build familiarity with two-pointer variants.

Signals

No signals fired — clean run, you stayed in flow.