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Tested Python solution for LeetCode 75 with 15 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 75 # by problem number
lcpy gen -s sort_colors # by problem name
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 the color red, white, and blue, respectively.
You must solve this problem without using the library’s sort function.
Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]
Input: nums = [2,0,1]
Output: [0,1,2]
n == nums.length1 <= n <= 300nums[i] is either 0, 1, or 2.class Solution:
# Dutch National Flag Algorithm - partitions array into 3 regions using 2 pointers
# Creates: [0s][1s][2s] with left/right boundaries, mid processes unvisited elements
# Time: O(n)
# Space: O(1)
def sort_colors(self, nums: list[int]) -> None:
left = mid = 0
right = len(nums) - 1
while mid <= right:
if nums[mid] == 0:
nums[left], nums[mid] = nums[mid], nums[left]
left += 1
mid += 1
elif nums[mid] == 1:
mid += 1
else:
nums[mid], nums[right] = nums[right], nums[mid]
right -= 1
| Time | Space |
|---|---|
| O(n) | O(1) |