75. Sort Colors(Solution || Leetcode medium || Java)

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:

class Solution {
    public void sortColors(int[] nums) {
//First we will use a loop to count the number of red and white
//objects, we will not count the number of blue objects as after 
//counting red and white the remaining objects will be blue
        int red = 0;
        int white = 0;
        
      for(int i = 0; i < nums.length; i++){
          if(nums[i] == 0){
              red++;
           }
          else if(nums[i] == 1){
              white++;
          }
      }
      
//Here, we are placing objects at their correct index  
        for(int i = 0; i < nums.length; i++){
            if(red != 0){
                nums[i] = 0;
                red--;
            }
            else if(white != 0){
                nums[i] = 1;
                white--;
            }
            else{
                nums[i] = 2;
            }
            
        }
    }
}

Runtime: 0 ms, faster than 100.00% of Java online submissions for Sort Colors.

Memory Usage: 42.3 MB, less than 63.07% of Java online submissions for Sort Colors.

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