Level:
Medium
题目描述:
Given an array with n objects colored red, white or blue, sort them in-place 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.
Example:
Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]
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 a one-pass algorithm using only constant space?
思路分析:
三路快排的思想,以1作为标志,比1小的放在一边,比1大的放在另一边一边,但是要注意的一点是大的元素交换后由于该元素没有和标志1作比较,因此需要i=i-1。
代码:
public class Solution{
public void sortColors(int []nums){
if(nums==null||nums.length==0)
return;
int left=0;
int right=nums.length-1;
for(int i=0;i<=right;i++){
if(nums[i]<1){
nums[i]=nums[left];
nums[left]=0;
left++;
}else if(nums[i]>1){
nums[i]=nums[right];
nums[right]=2;
right--;
i=i-1;//交换过来的元素没有和1比较过,所以i减一
}
}
}
}