Repo created

libs/search/algos.hpp

@@ -0,0 +1,80 @@
+#pragma once
+
+#include "base/base.hpp"
+
+#include <algorithm>
+#include <cstddef>
+#include <vector>
+
+namespace search
+{
+namespace impl
+{
+struct LS
+{
+  size_t prevDecreasePos, decreaseValue;
+  size_t prevIncreasePos, increaseValue;
+
+  LS(size_t i)
+  {
+    prevDecreasePos = i;
+    decreaseValue = 1;
+    prevIncreasePos = i;
+    increaseValue = 1;
+  }
+};
+}  // namespace impl
+
+template <typename T, typename OutIter, typename Comp>
+void LongestSubsequence(std::vector<T> const & in, OutIter out, Comp cmp)
+{
+  if (in.empty())
+    return;
+
+  std::vector<impl::LS> v;
+  v.reserve(in.size());
+  for (size_t i = 0; i < in.size(); ++i)
+    v.push_back(impl::LS(i));
+
+  size_t res = 1;
+  size_t pos = 0;
+  for (size_t i = 0; i < v.size(); ++i)
+  {
+    for (size_t j = i + 1; j < v.size(); ++j)
+    {
+      if (cmp.Less(in[i], in[j]) && v[i].increaseValue + 1 >= v[j].increaseValue)
+      {
+        v[j].increaseValue = v[i].increaseValue + 1;
+        v[j].prevIncreasePos = i;
+      }
+
+      if (cmp.Greater(in[i], in[j]) && v[i].decreaseValue + 1 >= v[j].decreaseValue)
+      {
+        v[j].decreaseValue = v[i].decreaseValue + 1;
+        v[j].prevDecreasePos = i;
+      }
+
+      size_t const m = std::max(v[j].increaseValue, v[j].decreaseValue);
+      if (m > res)
+      {
+        res = m;
+        pos = j;
+      }
+    }
+  }
+
+  bool increasing = true;
+  if (v[pos].increaseValue < v[pos].decreaseValue)
+    increasing = false;
+
+  while (res-- > 0)
+  {
+    *out++ = in[pos];
+
+    if (increasing)
+      pos = v[pos].prevIncreasePos;
+    else
+      pos = v[pos].prevDecreasePos;
+  }
+}
+}  // namespace search