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by Sumit Chourasia | Oct 31, 2020 | Category :coding | Tags : algorithm array data-structure leetcode medium

Sort Colors - Array - Medium - LeetCode

Sort Colors - Array - Medium - LeetCode

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.

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?
 

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]
Example 3:

Input: nums = [0]
Output: [0]
Example 4:

Input: nums = [1]
Output: [1]
 

Constraints:

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

public class Solution {
    public void SortColors(int[] nums) {
        int left = 0;
        int right = nums.Length-1;
        for(int i=0;i<=right;i++){
            
            while(nums[i]==2 && i<right){
                swap(ref nums[i], ref nums[right]);
                right--;
            }
            
            while(nums[i]==0 && i>left){
                swap(ref nums[i], ref nums[left]);
                left++;
            }                        
        }
    }
    
    private void swap(ref int a, ref int b){
        int temp = a;
        a = b;
        b = temp;
    }
}

Time Complexity: O(n)

Space Complexity: O(1)

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