STL 源碼剖析 演算法 stl_algo.h -- random_shuffle

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random_shuffle

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描述：將[first,last)的元素次序隨機重排。
思路：
必須是 RandomAccessIterator 
1.遍曆區間
2.產生[0,i)中的一個隨機數rand，將*(first+rand)與i交換
??怎麼證明隨機性 
源碼：

template <class RandomAccessIterator>inline void random_shuffle(RandomAccessIterator first,                           RandomAccessIterator last) {  __random_shuffle(first, last, distance_type(first));}template <class RandomAccessIterator, class RandomNumberGenerator>void random_shuffle(RandomAccessIterator first, RandomAccessIterator last,                    RandomNumberGenerator& rand) { //這裡必須是傳引用。因為隨機數產生器有局部狀態，每次被調用都會改變  if (first == last) return;  for (RandomAccessIterator i = first + 1; i != last; ++i)    iter_swap(i, first + rand((i - first) + 1));}template <class RandomAccessIterator, class Distance>void __random_shuffle(RandomAccessIterator first, RandomAccessIterator last,                      Distance*) {  if (first == last) return;  for (RandomAccessIterator i = first + 1; i != last; ++i) #ifdef __STL_NO_DRAND48    iter_swap(i, first + Distance(rand() % ((i - first) + 1)));#else  iter_swap(i, first + Distance(lrand48() % ((i - first) + 1)));#endif}

樣本：

int main(){vector<int> vec;for(int ix = 0; ix < 10; ix++)vec.push_back(ix);random_shuffle(vec.begin(), vec.end());copy(vec.begin(), vec.end(), ostream_iterator<int>(cout, " "));}