Sort Colors —— LeetCode

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?

题目大意：给一个只有0,1,2的数组，排序，不要用库函数。

解题思路：使用类似快排的思想，交换即可。其实可以one-pass的，写的不好，要遍历3遍。

public class Solution {
    public void sortColors(int[] nums) {
        if(nums==null||nums.length==0){
            return;
        }
        swap(nums,0,2);
        swap(nums,1,2);
        swap(nums,0,1);
    }
    private void swap(int[] nums,int sm,int lg){
        int i=0,j=nums.length-1;
        while(i<j){
            while(i<nums.length&&nums[i]!=lg){
                i++;
            }
            while(j>=0&&nums[j]!=sm){
                j--;
            }
            if(i<j){
                int t = nums[i];
                nums[i]=nums[j];
                nums[j]=t;
            }
        }
    }
}