本文实例讲述了C++实现查找中位数的O(N)算法和Kmin算法，分享给大家供大家参考。具体方法如下：
利用快速排序的partition操作来完成O(N)时间内的中位数的查找算法如下：
#include <iostream>
#include <cassert>
#include <algorithm>
#include <iterator>
using namespace std;
int array[] = {1, 2, 10, 8, 9, 7, 5};
const int size = sizeof array / sizeof *array;
int partition(int *array, int left, int right)
{
if (array == NULL)
return -1;
int pos = right;
right--;
while (left <= right)
{
while (left < pos && array[left] <= array[pos])
left++;
while (right >= 0 && array[right] > array[pos])
right--;
if (left >= right)
break;
swap(array[left], array[right]);
}
swap(array[left], array[pos]);
return left;
}
int getMidIndex(int *array, int size)
{
if (array == NULL || size <= 0)
return -1;
int left = 0;
int right = size - 1;
int midPos = right >> 1;
int index = -1;
while (index != midPos)
{
index = partition(array, left, right);
if (index < midPos)
{
left = index + 1;
}
else if (index > midPos)
{
right = index - 1;
}
else
{
break;
}
}
assert(index == midPos);
return array[index];
}
void main()
{
int value = getMidIndex(array, size);
cout << "value: " << value << endl;
}
寻找kmin算法如下：
int findKMin(int *array, int size, int k)
{
if (array == NULL || size <= 0)
return -1;
int left = 0;
int right = size - 1;
int index = -1;
while (index != k)
{
index = partition(array, left, right);
if (index < k)
{
left = index + 1;
}
else if (index > k)
{
right = index - 1;
}
else
{
break;
}
}
assert(index == k);
return array[index];
}
希望本文所述对大家C++程序算法设计的学习有所帮助。
