75. Sort Colors

 

75. Sort Colors

Medium

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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?

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Submissions

860,703

第一次用的冒泡排序，结果也还可以，第二次参考别人的代码如下

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

class Solution {
public:
    void sortColors(vector<int>& nums) {//冒泡
        for(int i=0;i<nums.size();i++){
            for(int j=i+1;j<nums.size();j++){
                if(nums[i]>nums[j]) swap(nums[i],nums[j]);
            }
        }
    }
};