Added Fisher-Yates shuffle and partial-shuffle

src/Common/shuffle.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <iterator>
+#include <random>
+#include <utility>
+
+/* Reorders the elements in the given range [first, last) such that each
+ * possible permutation of those elements has equal probability of appearance.
+ */
+template <typename Iter, typename Rng>
+void shuffle(Iter first, Iter last, Rng && rng)
+{
+    using diff_t = typename std::iterator_traits<Iter>::difference_type;
+    using distr_t = std::uniform_int_distribution<diff_t>;
+    using param_t = typename distr_t::param_type;
+    distr_t d;
+    diff_t n = last - first;
+    for (ssize_t i = 0; i < n - 1; ++i)
+    {
+        using std::swap;
+        auto j = d(rng, param_t(i, n - 1));
+        swap(first[i], first[j]);
+    }
+}
+
+
+/* Partially shuffle elements in range [first, last) in such a way that
+ * [first, first + limit) is a random subset of the original range.
+ * [first + limit, last) shall contain the elements not in [first, first + limit)
+ * in undefined order.
+ */
+template <typename Iter, typename Rng>
+void partial_shuffle(Iter first, Iter last, size_t limit, Rng && rng)
+{
+    using diff_t = typename std::iterator_traits<Iter>::difference_type;
+    using distr_t = std::uniform_int_distribution<diff_t>;
+    using param_t = typename distr_t::param_type;
+    distr_t d;
+    diff_t n = last - first;
+    for (size_t i = 0; i < limit; ++i)
+    {
+        using std::swap;
+        auto j = d(rng, param_t(i, n - 1));
+        swap(first[i], first[j]);
+    }
+}