[Solved] 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 the color red, white, and blue, respectively.

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Question

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 01, and 2 to represent the color red, white, and blue, respectively.

You must solve this problem without using the library’s sort function.

Example 1:

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

Example 2:

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

Constraints:

  • n == nums.length
  • 1 <= n <= 300
  • nums[i] is either 01, or 2.

Follow up: Could you come up with a one-pass algorithm using only constant extra space?

Python Solution

class Solution:
    def sortColors(self, A: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        l = 0
        r = len(A)-1
        scan = 0
        
        while scan<=r:
            if A[scan]==0:
                A[scan],A[l] = A[l],A[scan]
                l+=1
                scan+=1
            elif A[scan]==2:
                A[scan],A[r] = A[r],A[scan]
                r-=1
            else:
                scan+=1
        return(A)

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