package cn.fmachine.leetcode.medium;

/**
 * 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.
 * <p>
 * Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.
 * <p>
 * Note:
 * You are not suppose to use the library's sort function for this problem.
 * <p>
 * click to show follow up.
 * <p>
 * Follow up:
 * A rather straight forward solution is a two-pass algorithm using counting sort.
 * First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's, then 1's and followed by 2's.
 * <p>
 * Could you come up with an one-pass algorithm using only constant space?
 * <p>
 * algorithm
 * Author: XIN MING
 * Date: 7/29/17
 */
public class SortColors {
    /**
     * O(n)
     * O(1)
     */
    public void sortColors(int[] nums) {
        int left = 0; // index for 0
        int right = nums.length - 1; // index for 2
        for (int i = 0; i <= right; i++) { // stop at right, otherwise, result will be 002211
            if (nums[i] == 0) {
                swap(nums, i, left++);
            } else if (nums[i] == 2) {
                swap(nums, i--, right--); // check same place again
            }
            // leave 1 in the middle
        }
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }

}
