Basic sorting algorithm Summary + LeetCode_75. Color Classification

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Description Title:
Given a red, white and blue, a total of n elements of the array, sorts them in situ, such that adjacent elements with the same color and arranged in a red, white, blue order.

This question, we use an integer of 0, 1 and 2 represent the red, white and blue.

Note:
You can not use the sort function code base to solve this question.

Example:

Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

1, bubble sort

class Solution {
public:
    void sortColors(vector<int>& nums) {
        if(nums.empty())
            return ;
        int n=nums.size();
        for(int i=n-1;i>0;i--){
            bool flag=false;//标记,如果本轮没发生交换,则有序，不需要再排
            for(int j=n-1;j>n-1-i;j--){//每次都是从最后往前比较
                if(nums[j]<nums[j-1]){
                    flag=true;
                    swap(nums[j],nums[j-1]);
                }
            }
            if(flag==false)
                return ;
        }
    }
};