[LintCode] Median（期望时间复杂度O(n)求中位数）

 1 class Solution {
 2 public:
 3     /**
 4      * @param nums: A list of integers.
 5      * @return: An integer denotes the middle number of the array.
 6      */
 7     void swap(vector<int> &v, int i, int j)
 8     {
 9         int tmp = v[i];
10         v[i] = v[j];
11         v[j] = tmp;
12     }
13     int getMedian(vector<int> &v, int left, int right)
14     {
15         if(left<right)
16         {
17             int i = left-1, j = left;
18             for(; j<right;  ++j)
19             {
20                 if(v[j]<v[right])
21                 {
22                     ++i;
23                     swap(v, i, j);
24                 }
25             }
26             swap(v, i+1, right);
27             int sz = v.size();
28             if((sz-1)/2==i+1) return v[i+1];
29             else if((sz-1)/2<=i)  return getMedian(v, left, i);
30             else    return getMedian(v, i+2, right);
31         }
32         else    return v[left];
33     }
34     int median(vector<int> &v) {
35         // write your code here
36         return getMedian(v, 0, v.size()-1);
37     }
38 };