75. Sort Colors

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?

 

0,1,2排序

 

C++：

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int left = 0 ;
        int right = nums.size()-1 ;
        for(int i = 0 ; i <= right ;){
            if (nums[i] == 0){
                swap(nums[i],nums[left++]) ;
                i++;
            }else if (nums[i] == 2){
                swap(nums[i],nums[right--]) ;
            }else{
                i++ ;
            }
        }
    }
};