①push_heap算法
以下是push_heap算法的实现细节。该函数接收两个迭代器,用来表现一个heap底部容器(vector)的头尾,而且新元素已经插入究竟部的最尾端。
template <class RandomAccessIterator>
inline void push_heap(RandomAccessIterator first,RandomAccessIterator last)
{
//注意,此函数被调用时,新元素应已置于底部容器的最尾端
_push_heap_aux(first,last,distance_type(first),value_type(first));
}
template <class RandomAccessIterator,class Distance,class T>
inline void _push_heap_aux(RandomAccessIterator first,RandomAccessIterator last,
Distance*,T*)
{
//以上系依据heap的结构特性:新值必置于底部容器的最尾端,此即第一个洞号:(last-first)-1
_push_heap(first,Distance((last-first)-1),Distance(0),T(*(last-1)));
}
template <class RandomAccessIterator,class Distance,class T>
void _push_heap(RandomAccessIterator first,Distance holeIndex,Distance topIndex,T value)
{
Distance parent = (holeIndex-1)/2;
while (parent > topIndex && *(first+parent)<value)
{
*(first + holeIndex) = *(first + parent);
holeIndex = parent;
parent = (holeIndex-1)/2;
}
*(first + holeIndex) = value;
}
②pop_heap算法
pop操作取走根节点(事实上是设至底部容器vector的尾端节点)后,为了满足complete binary tree的条件,必须割舍最下层最右边的叶节点,并将其值又一次安插至最大堆。
template <class RandomAccessIterator>
inline void pop_heap(RandomAccessIterator first,RandomAccessIterator last)
{
_pop_heap_aux(first,last,value_type(first));
}
template <class RandomAccessIterator,class T>
inline void _pop_heap_aux(RandomAccessIterator first,RandomAccessIterator last,T*)
{
_pop_heap(first,last-1,last-1,T(*(last-1)),distance_type(first));
}
template <class RandomAccessIterator,class T,class Distance>
inline void _pop_heap(RandomAccessIterator first,RandomAccessIterator last,RandomAccessIterator result,
T value,Distance*)
{
*result = *first;
_adjust_heap(first,Distance(0),Distance(last-first),value);
//以上欲又一次调整heap,洞号为0(亦即树根处),欲调整值为value(原尾值)
}
template <class RandomAccessIterator,class Distance,class T>
void _adjust_heap(RandomAccessIterator first,Distance holeIndex,Distance len,T value)
{
Distance topIndex = holeIndex;
Distance secondChild = holeIndex*2+2;
while (secondChild < len)
{
if(*(first+secondChild) < *(first+secondChild-1))
secondChild–;
*(first+holeIndex) = *(first+secondChild);
holeIndex = secondChild;
secondChild = holeIndex*2+2;
}
if (secondChild == len)
{
*(first+holeIndex) = *(first+secondChild-1);
holeIndex = secondChild-1;
}
_push_heap(first,holeIndex,topIndex,value);
}
注意:pop_heap之后,最大元素仅仅是被置于底部容器的最尾端,尚未被取走。假设要取其值,可使用底部容器(vector)所提供的back()操作函数。假设要移除它,可使用底部容器(vector)所提供的pop_back()操作函数。
③sort_heap算法
既然每次pop_heap可获得heap中键值最大的元素,假设持续对整个heap做pop_heap操作,每次将操作范围从后向前缩减一个元素(由于pop_heap会把键值最大的元素放在底部容器的最尾端),当整个程序运行完成时,我们便有了一个递增序列。
template<class RandomAccessIterator>
void sort_heap(RandomAccessIterator first,RandomAccessIterator last)
{
while(last – first > 1)
pop_heap(first,last–);
}
④make_heap算法
这个算法用来将一段现有的数据转化为一个heap。
template <class RandomAccessIterator>
inline void make_heap(RandomAccessIterator first,RandomAccessIterator last)
{
_make_heap(first,last,value_type(first),distance_type(first));
}
template <class RandomAccessIterator,class T,class Distance>
void _make_heap(RandomAccessIterator first,RandomAccessIterator last,T*,Distance*)
{
if (last – first < 2) return;
Distance len = last-first;
Distance parent = (len-1)/2;
while (true)
{
_adjust_heap(first,parent,len,T(*(first+parent)));
if (parent == 0)
return;
parent–;
}
}
发布者:全栈程序员-用户IM,转载请注明出处:https://javaforall.cn/119095.html原文链接:https://javaforall.cn
【正版授权,激活自己账号】: Jetbrains全家桶Ide使用,1年售后保障,每天仅需1毛
【官方授权 正版激活】: 官方授权 正版激活 支持Jetbrains家族下所有IDE 使用个人JB账号...