数据结构练习（04）查找最小的k个元素

http://zhedahht.blog.163.com/blog/static/2541117420072432136859/

#include <iostream>
#include <vector>
#include <set>
using namespace std;

void findknumbers(const vector<int>& data, multiset<int, greater<int>>& leastheap, int k)
{
    leastheap.clear();

    if (k == 0 || data.size() < k)
        return;

    vector<int>::const_iterator iter = data.begin();
    for (; iter != data.end(); ++iter)
    {
        if (leastheap.size() < k)
            leastheap.insert(*iter);
        else
        {
            multiset<int, greater<int>>::iterator iterfirst = leastheap.begin();
            if (*iter < *(leastheap.begin()))
            {
                leastheap.erase(iterfirst);
                leastheap.insert(*iter);
            }
        }
    }
}

int main()
{
    vector<int> data;
    for (int i = 100; i >= 0; --i)
        data.push_back(i);
    
    multiset<int, greater<int>> leastheap;

    findknumbers(data, leastheap, 10);

    multiset<int, greater<int>>::const_iterator iter = leastheap.begin();
    for (; iter != leastheap.end(); ++iter)
        cout << *iter << ' ';

    return 0;
}

 自己写的：

#include <cstdio>
#include <cstdlib>
#include <cstring>

int data[110];
int maxheap[110];
int heapsize;

void swap(int &a, int &b)
{
    int t = a;
    a = b, b = t;
}

void maxheapfixup(int i)
{
    int j = i >> 1;
    while (j >= 1 && i > 1)
    {
        if (maxheap[j] >= maxheap[i])
            break;
        swap(maxheap[i], maxheap[j]);
        i = j;
        j = i >> 1;
    }
}

void maxheapfixdown(int i)
{
    int left = i << 1;

    while (left <= heapsize)
    {
        int p = left;
        int right = left + 1;

        if (right <= heapsize && maxheap[left] < maxheap[right])
            p = right;

        if (maxheap[i] >= maxheap[p])
            break;

        swap(maxheap[i], maxheap[p]);
        i = p;
        left = i << 1;
    }
}

void heapinsert(int n, int num)
{
    maxheap[n] = num;
    maxheapfixup(n);
}

void findknumber(int n, int k)
{
    heapsize = k;

    for (int i = 1; i <= heapsize; ++i)
        heapinsert(i, data[i]);

    for (int i = heapsize + 1; i <= n; ++i)
        if (data[i] < maxheap[1])
            maxheap[1] = data[i], maxheapfixdown(1);
}

int main()
{
    for (int i = 1; i <= 100; ++i)
        data[i] = 101 - i;

    findknumber(100, 10);

    for (int i = 1; i <= heapsize; ++i)
        printf("%d ", maxheap[i]);

    return 0;
}