Sort Colors


Problem Statement :


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.

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 0, 1, or 2.
 

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


Solution :



title-img 


                            Solution in C :

void sortColors(int* nums, int numsSize){
    int two_ptr = numsSize -1;
    int zero_ptr = 0;
    int one_ptr = 0;
    while (one_ptr <= two_ptr)
    {
        if (nums[one_ptr] == 0)
        {
            int save = nums[zero_ptr];
            nums[zero_ptr] = nums[one_ptr];
            nums[one_ptr] = save;
            one_ptr++; zero_ptr++;
        }
        else if (nums[one_ptr] == 1)
        {
            one_ptr++;
        }
        else
        {
            int save = nums[two_ptr];
            nums[two_ptr] = nums[one_ptr];
            nums[one_ptr] = save;
            two_ptr--;
        }
    }
}
                        


                        Solution in C++ :

class Solution {
    public void sortColors(int[] nums) {
        int count0s = 0;
        int count1s = 0;
        int count2s = 0;
        
        for (int i = 0; i <nums.length ; i++) {
            if (nums[i]==0)count0s++;
            else if (nums[i]==1)count1s++;
            else if (nums[i]==2)count2s++;
        }
        count1s += count0s;
        count2s += count1s;
        for (int i = 0; i < nums.length; i++) {
            if (i<count0s)nums[i] = 0;
            else if (i<count1s)nums[i] = 1;
            else if (i<count2s)nums[i] = 2;
        }
    }
}
                    


                        Solution in Java :

class Solution {
    public void sortColors(int[] nums) {
        int low=0;
        int mid=0;
        int high=nums.length-1;
        while(mid<=high){
            if(nums[mid]==0){
                swap(nums,low,mid);
                low++;
                mid++;
            }else if(nums[mid]==1){
                mid++;
            }else{
                swap(nums,mid,high);
                high--;
            }
        }
        
    }
    private void swap(int[] nums,int i, int j){
        int temp=nums[i];
        nums[i]=nums[j];
        nums[j]=temp;
    }
}
                    


                        Solution in Python : 
                            
class Solution:
    def sortColors(self, nums: List[int]) -> None:
        for i in range(0,len(nums)-1):
            for j in range(0,len(nums)-i-1):
                if nums[j] > nums[j+1]:
                    nums[j], nums[j+1] = nums[j+1], nums[j]


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