[leetcode] 75. Sort Colors

Description

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?

分析

题目的意思是：给定一个只包含0，1，2无序的数组，求只经过一次便利能够让数组有序。

• 很明显，0要放前面，2要放后面，便利数组，如果遇见0就提前，遇见2就往后，1的话就跳过。

代码

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

参考文献

​​75. Sort Colors​​