CODE 58. Sort Colors

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/10/04/2013-10-04-CODE 58 Sort Colors/

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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.
click to show follow up.
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.
Could you come up with an one-pass algorithm using only constant space?

WORST CODE:

public void sortColors(int[] A) {
	// Note: The Solution object is instantiated only once and is reused by
	// each test case.
	// 012012012012
	int start = 0;
	int end = A.length - 1;
	while (start < A.length && A[start] == 0) {
		start++;
	}
	while (end > 0 && A[end] == 2) {
		end--;
	}
	for (int mid = start; mid <= end; mid++) {
		if (A[mid] == 0) {
			int tmp = A[mid];
			A[mid] = A[start];
			A[start] = tmp;
			start++;
			while (start < A.length && A[start] == 0) {
				start++;
			}
			mid = start - 1;
		} else if (mid != end && A[mid] == 2) {
			int tmp = A[mid];
			A[mid] = A[end];
			A[end] = tmp;
			end--;
			mid--;
			while (end > 0 && A[end] == 2) {
				end--;
			}
		}
	}
}