add forgotten file again

llarp/util/algorithm.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <algorithm>
+
+namespace llarp::util
+{
+  /// remove items from a container if a predicate is true
+  /// return the number of items removed
+  constexpr auto erase_if = [](auto& container, auto&& pred) -> std::size_t {
+    std::size_t removed = 0;
+    for (auto itr = container.begin(); itr != container.end();)
+    {
+      if (pred(*itr))
+      {
+        itr = container.erase(itr);
+        removed++;
+      }
+      else
+        itr++;
+    }
+    return removed;
+  };
+}  // namespace llarp::util