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.

Solution

0 0 0 1 1 1 1 ...... 2 2 2 2
   |         |      |
 zero        i     two
  ->        ->     <-

荷兰国旗问题

Complexity

时间复杂度 O(n)，空间复杂度 O(1)

Code

public class Solution {
    public void sortColors(int[] A) {
        int n = A.length;
        if (n <= 1) return;
        for (int i = 0, left = 0, right = n - 1; i <= right;) {
            if (A[i] == 0) {
                A[i++] = A[left];
                A[left++] = 0;
            } else if (A[i] == 2) {
                A[i] = A[right];
                A[right--] = 2;
            } else 
                i++;
        }
    }
}