Problem

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.

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

Constraints:

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

Follow up:

• Could you solve this problem without using the library’s sort function?
• Could you come up with a one-pass algorithm using only O(1) constant space?

Example1

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

Example2

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

Example3

Input: nums = [0]
Output: [0]

Example4

Input: nums = [1]
Output: [1]

Solution

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int i = 0;
        int j = 0;
        int k = nums.size() - 1;

        while(i <= k)
        {
            if(nums[i] == 0)
            {
                swap(nums[i++],nums[j++]);
            }
            else if(nums[i] == 1)
            {
                ++i;
            }
            else{
                swap(nums[i],nums[k--]);
            }
        }
        
    }
};