From 71de01065bef7c128e740f28d6b160be320b6d8f Mon Sep 17 00:00:00 2001
From: Mat Sutcliffe <oktal3700@gmail.com>
Date: Tue, 11 Dec 2018 17:12:09 +0000
Subject: [PATCH] Ref T464 Implement removal of one sequence from another in
 O(n), assuming that elements in both sequences are in the same order in both.

---
 src/blackgui/views/viewbase.cpp               |  5 +----
 src/blackmisc/algorithm.h                     | 21 +++++++++++++++++++
 src/blackmisc/sequence.h                      |  7 +++++++
 .../testcontainers/testcontainers.cpp         | 18 ++++++++++++++++
 4 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/src/blackgui/views/viewbase.cpp b/src/blackgui/views/viewbase.cpp
index 21db85c54..07cad5cd3 100644
--- a/src/blackgui/views/viewbase.cpp
+++ b/src/blackgui/views/viewbase.cpp
@@ -340,10 +340,7 @@ namespace BlackGui
             else
             {
                 ContainerType unselectedObjects(container());
-                for (const ObjectType &obj : selected)
-                {
-                    unselectedObjects.remove(obj);
-                }
+                unselectedObjects.removeIfInSubset(selected);
                 this->updateContainerMaybeAsync(unselectedObjects);
                 delta = currentRows - unselectedObjects.size();
             }
diff --git a/src/blackmisc/algorithm.h b/src/blackmisc/algorithm.h
index df6a84540..74e712e63 100644
--- a/src/blackmisc/algorithm.h
+++ b/src/blackmisc/algorithm.h
@@ -22,6 +22,27 @@
 
 namespace BlackMisc
 {
+    /*!
+     * Removes those elements in range 1 that appear also in range 2 leaving only those that
+     * do not appear in range 2. Returns an iterator one past the new end of range 1.
+     * \pre All the elements of range 2 must be present in the same order in range 1.
+     */
+    template <typename I, typename J>
+    auto removeIfIn(I begin1, I end1, J begin2, J end2)
+    {
+        auto newEnd = end1;
+        std::for_each(begin2, end2, [&](const auto &rm)
+        {
+            const auto found = std::find(begin1, end1, rm);
+            Q_ASSERT(found != end1);
+            if (newEnd == end1) { newEnd = found; }
+            else { newEnd = std::move(begin1, found, newEnd); }
+            begin1 = std::next(found);
+        });
+        if (newEnd != end1) { newEnd = std::move(begin1, end1, newEnd); }
+        return newEnd;
+    }
+
     namespace Private
     {
         //! \private A high quality deterministic pseudo-random number generator.
diff --git a/src/blackmisc/sequence.h b/src/blackmisc/sequence.h
index 4e2d9bb48..666aea2b1 100644
--- a/src/blackmisc/sequence.h
+++ b/src/blackmisc/sequence.h
@@ -321,6 +321,13 @@ namespace BlackMisc
             return removeIf([&other](const T &v) { return other.contains(v); });
         }
 
+        //! Remove all elements if they are in other
+        //! \pre All elements of other must be present in the same order in this.
+        void removeIfInSubset(const CSequence &other)
+        {
+            erase(BlackMisc::removeIfIn(begin(), end(), other.begin(), other.end()), end());
+        }
+
         //! Replace elements matching the given element with a replacement.
         //! \return The number of elements replaced.
         int replace(const T &original, const T &replacement)
diff --git a/tests/blackmisc/testcontainers/testcontainers.cpp b/tests/blackmisc/testcontainers/testcontainers.cpp
index e478d8975..cdd6f8fdc 100644
--- a/tests/blackmisc/testcontainers/testcontainers.cpp
+++ b/tests/blackmisc/testcontainers/testcontainers.cpp
@@ -65,6 +65,7 @@ namespace BlackMiscTest
         void joinAndSplit();
         void findTests();
         void sortTests();
+        void removeTests();
         void dictionaryBasics();
         void timestampList();
         void offsetTimestampList();
@@ -199,6 +200,23 @@ namespace BlackMiscTest
         QVERIFY2(list.sortedBy(&Person::getAge, &Person::getName) == sorted, "sort by multiple members");
     }
 
+    void CTestContainers::removeTests()
+    {
+        const CSequence<int> base { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+        const CSequence<CSequence<int>> subsets
+        {
+            {}, { 1 }, { 9 }, { 5 }, { 1, 9 }, { 1, 5 }, { 5, 9 }, { 1, 2 },
+            { 8, 9 }, { 4, 5, 6 }, { 1, 5, 9 }, { 3, 7 }, { 3, 5, 7 }, base
+        };
+        for (const auto &subset : subsets)
+        {
+            auto copy1 = base, copy2 = base;
+            copy1.removeIfIn(subset);
+            copy2.removeIfInSubset(subset);
+            QVERIFY2(copy1 == copy2, "removeIfInSubset");
+        }
+    }
+
     void CTestContainers::dictionaryBasics()
     {
         CTestValueObject key1("Key1", "This is key object 1");