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.
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?
https://oj.leetcode.com/problems/sort-colors/
思路1： counting sort. 如题目中所示，需要2 passes。
思路2：双指针法。（其实是algorithms里讲的的quicksort中的three-way-partition部分，详见这里）
思路2代码
import java.util.Arrays; public class Solution { public void sortColors(int[] A) { if (A == null || A.length <= 1) return; int n = A.length; int lt = 0; int gt = n - 1; int i = 0; while (i <= gt) { if (A[i] == 1) { i++; } else if (A[i] == 0) { swap(A, lt++, i++); } else { swap(A, gt--, i); } } } private void swap(int[] a, int i, int j) { int tmp = a[i]; a[i] = a[j]; a[j] = tmp; } public static void main(String[] args) { int[] A = { 1, 0, 2, 0, 1 }; new Solution().sortColors(A); System.out.println(Arrays.toString(A)); } }
[leetcode] Sort Colors,布布扣,bubuko.com
原文：http://www.cnblogs.com/jdflyfly/p/3815231.html
