Leetcode sort colors

Leetcode-Sort colors

Given an array with n objects colored red, white or blue, sort them 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.

Note:
You are not suppose to use the library's sort function for this problem.

Train of Thought Analysis: This question is very simple, but it is difficult to make O (n) time complex and use only the constant memory. The O (n) solution includes bucket sorting and counting sort, the former requires extra space of O (n), and the latter requires only the constant memory. The AC code based on counting sort is provided here.

AC code:

public class Solution {    public void sortColors(int[] A) {        //Implement counting sort        int count1 = 0;         int count2 = 0;         int count0 = 0;        for(int i = 0; i < A.length; i++){            if(A[i] == 2){                count2++;            } else if(A[i] == 1){                count1++;                swap(A, i , i-count2);            } else {                count0++;                swap(A, i, i-count2);                swap(A, i-count2, i-count2-count1);            }        }    }        public void swap(int[] A, int i, int j){        int temp;        temp = A[i];        A[i] = A[j];        A[j] = temp;    }}

Leetcode sort colors