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template<class _RanIt,
class _Diff> inline
void _Random_shuffle(_RanIt _First, _RanIt _Last, _Diff *)
{ // shuffle [_First, _Last)
_DEBUG_RANGE(_First, _Last);
const int _RANDOM_BITS = 15; // minimum random bits from rand()
const int _RANDOM_MAX = (1U << _RANDOM_BITS) - 1;
_RanIt _Next = _First;
for (unsigned long _Index = 2; ++_Next != _Last; ++_Index)
{ // assume unsigned long big enough for _Diff count
unsigned long _Rm = _RANDOM_MAX;
unsigned long _Rn = ::rand() & _RANDOM_MAX;
for (; _Rm < _Index && _Rm != ~0UL;
_Rm = _Rm << _RANDOM_BITS | _RANDOM_MAX)
_Rn = _Rn << _RANDOM_BITS
| (::rand() & _RANDOM_MAX); // build random value
std::iter_swap(_Next, _First + _Diff(_Rn % _Index)); // swap a pair
}
}
template<typename _RandomAccessIterator>
inline void
random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last)
{
if (__first != __last)
for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
std::iter_swap(__i, __first + (std::rand() % ((__i - __first) + 1)));
}
我觉得 vs2008 和 g++-4.8.0 都是正确的,和主楼贴出的网页中给的第二种方法本质一样。
随机洗牌算法的重点是随机区间要随着当前元素移动,至于是左区间还是右区间到不是太重要,因为在区间顺序倒换的情况下,两者是等价的。