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random_shuffle

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描写叙述：将[first,last)的元素次序随机重排。

思路：

必须是 RandomAccessIterator 

1.遍历区间

2.产生[0,i)中的一个随机数rand。将*(first+rand)与i交换

??怎么证明随机性 

源代码：

template 
     
      inline void random_shuffle(RandomAccessIterator first,                           RandomAccessIterator last) {  __random_shuffle(first, last, distance_type(first));}template 
      
       void random_shuffle(RandomAccessIterator first, RandomAccessIterator last,                    RandomNumberGenerator& rand) { //这里必须是传引用。
      
     

由于随机数产生器有局部状态。每次被调用都会改变 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 }

演示样例：

int main(){	vector
     
       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
      
       (cout, " "));}