归并排序

归并排序

class Solution {
public:
    void mergesort(vector<int>  &data) 
    {
        
    }
    
    void merge1(vector<int>  &data, int start, int end)
    {
        int ret = end -start;
        if (0 == ret)
            return;
        else if ( 1 == ret)
        {
            if (data[start] > data[end])
            {
                data[start] ^= data[end];
                data[end]   ^= data[start];
                data[start] ^= data[end];
            }
        }
        else
        {
            int middle = (start + end)/2;
            merge1(data, start, middle);
            merge1(data, middle+1, end);
            vector<int > res = merge2(data, start, end);
            for (int i=0;i<res.size();i++)
                data[start + i] = res[i];
        }
    }
    vector<int>  merge2(vector<int>  &data, int start, int end)
    {
        vector <int> res;
        int middle = (start + end)/2;
        int left  = start;
        int right = middle + 1;
        while(left <= middle && right <= end)
        {
            if (data[left] < data[right])
                res.push_back(data[left++]);
            else
                res.push_back(data[right++]);
        }
        while(left <= middle)
            res.push_back(data[left++]);
        while(right <= end)
            res.push_back(data[right++]);
    }
};