从 STL 范围中获取 [伪] 随机元素的好方法是什么?
What is a good way to get a [pseudo-]random element from an STL range?
我能想到的最好方法是做 std::random_shuffle(c.begin(), c.end()) 然后从 c.begin 中取出我的随机元素().
The best I can come up with is to do std::random_shuffle(c.begin(), c.end()) and then take my random element from c.begin().
但是,我可能想要一个来自 const 容器的随机元素,或者我可能不想要完全 shuffle 的成本.
However, I might want a random element from a const container, or I might not want the cost of a full shuffle.
有更好的方法吗?
推荐答案我在 Google+ 的一篇文章中发布了这个解决方案,其他人引用了这个.把它贴在这里,因为这个比其他的稍微好一点,因为它通过使用 std::uniform_int_distribution 避免了偏见:
I posted this solution on a Google+ article where someone else referenced this. Posting it here, as this one is slightly better than others because it avoids bias by using std::uniform_int_distribution:
#include <random> #include <iterator> template<typename Iter, typename RandomGenerator> Iter select_randomly(Iter start, Iter end, RandomGenerator& g) { std::uniform_int_distribution<> dis(0, std::distance(start, end) - 1); std::advance(start, dis(g)); return start; } template<typename Iter> Iter select_randomly(Iter start, Iter end) { static std::random_device rd; static std::mt19937 gen(rd()); return select_randomly(start, end, gen); }示例用途是:
#include <vector> using namespace std; vector<int> foo; /* .... */ int r = *select_randomly(foo.begin(), foo.end());我最终创建了一个遵循类似方法并具有更好设计的要点.
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