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.

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?

题意：给定一个数组，里面有红色，白色，蓝色，我们用0,1,2分别代表这三种颜色

排序，要求按照红色，白色，蓝色的顺序  

分类：数组，双指针，排序

解法1：直接使用排序算法进行排序

[java] view plain copy

1. public class Solution {  
2.     public void sortColors(int[] nums) {  
3.         Arrays.sort(nums);  
4.     }      
5. }  

解法2：双指针，分别执行start,end

另外还有一个cur指针去遍历数组，当cur遇到白色，就和start交换

注意，start如果在cur之前，就说明它已经是白色的了，所以此时要不需要交换，cur++即可

同理，如果遇到蓝色，和end交换，也要注意这个问题

否则，cur++

[java] view plain copy

1. public class Solution {  
2.     public void sortColors(int[] nums) {  
3.         int cur = 0;  
4.         int len = nums.length;  
5.         int start = 0;  
6.         int end = len-1;  
7.         while(cur<len){  
8.             if(nums[cur]==0){  
9.                 if(cur>start){  
10.                     swap(nums, cur, start);  
11.                     start++;  
12.                 }else{  
13.                     cur++;  
14.                 }  
15.             }else if(nums[cur]==2){  
16.                 if(cur<end){  
17.                     swap(nums, cur, end);  
18.                     end--;  
19.                 }else{  
20.                     cur++;  
21.                 }  
22.             }else{  
23.                 cur++;  
24.             }  
25.         }  
26.     }  
27.       
28.     public void swap(int[] nums,int i,int j){  
29.         int t = nums[i];  
30.         nums[i] = nums[j];  
31.         nums[j] = t;  
32.     }  
33. }  

原文链接http://blog.csdn.net/crazy__chen/article/details/46419991