[剑指Offer] 29.最小的K个数

【思路1】全排序（快排）之后取出前K个数。O(K+nlogn)

class Solution
{
public:
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k)
    {
        vector<int> res;
        if(k > input.size())
            return res;
        sort(input.begin(),input.end());
        for(int i = 0; i < k; i ++)
            res.push_back(input[i]);
        return res;
    }
};

【思路2】冒泡排序的思想，但不用全排序，只要找出K个即可

class Solution
{
public:
    void swap(int& x,int& y)
    {
        int temp = x;
        x = y;
        y = temp;
    }
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k)
    {
        vector<int> res;
        int size = input.size();
        if(k > size)
            return res;
        for(int i = 0; i < k; i ++)
        {
            for(int j = 0; j < size - i - 1; j ++)
            {
                if(input[j + 1] > input[j])
                {
                    swap(input[j + 1],input[j]);
                }
            }
            res.push_back(input[size - i - 1]);
        }
        return res;
    }
};