选择第K个最小元素

 1 int  partition(int int_array[], int low, int high) 
 2 {
 3     int first = low, last = high;
 4     int key = int_array[first];
 5 
 6     while(first < last)
 7     {
 8         while(first < last && int_array[last] >= key) --last;
 9         int_array[first] = int_array[last];
10         while(first < last && int_array[first] <= key) first++;
11         int_array[last] = int_array[first];
12     }
13     int_array[first] = key;
14     return first;
15 }
16 
17 int select(int a[], int low, int high, int k)
18 {
19         int index = partition(a, low, high);
20         if(index == k)
21             return a[index];
22         else 
23         {
24             if(k < index)
25                 select(a, low, index-1, k);
26             else
27                 select(a, index+1, high, k-index);
28         }
29 }