From c0cd7d2b3a3e9507648ad9b5a5bb24bce92805a0 Mon Sep 17 00:00:00 2001
From: Alexey Kudravtsev <cdr@intellij.com>
Date: Thu, 13 Dec 2018 14:06:31 +0300
Subject: [PATCH] small optimization: more efficient intersection, cleanup

---
 .../util/containers/ContainerUtil.java        | 27 ++++++++++---------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/platform/util/src/com/intellij/util/containers/ContainerUtil.java b/platform/util/src/com/intellij/util/containers/ContainerUtil.java
index b3b4a2921db3..1fc645e6190f 100644
--- a/platform/util/src/com/intellij/util/containers/ContainerUtil.java
+++ b/platform/util/src/com/intellij/util/containers/ContainerUtil.java
@@ -601,15 +601,18 @@ public class ContainerUtil extends ContainerUtilRt {
   @NotNull
   @Contract(pure=true)
   public static <K, V> Map<K, V> intersection(@NotNull Map<? extends K, ? extends V> map1, @NotNull Map<? extends K, ? extends V> map2) {
-    final Set<K> keys = new HashSet<K>();
-    keys.addAll(map1.keySet());
-    keys.addAll(map2.keySet());
-    final Map<K, V> res = new HashMap<K, V>();
-    for (K k : keys) {
-      V v1 = map1.get(k);
-      V v2 = map2.get(k);
-      if (v1 == v2 || v1 != null && v1.equals(v2)) {
-        res.put(k, v1);
+    if (map2.size() < map1.size()) {
+      Map<? extends K, ? extends V> t = map1;
+      map1 = map2;
+      map2 = t;
+    }
+    final Map<K, V> res = new HashMap<K, V>(map1);
+    for (Map.Entry<? extends K, ? extends V> entry : map2.entrySet()) {
+      K key = entry.getKey();
+      V v2 = entry.getValue();
+      V v1 = map1.get(key);
+      if (!(v1 == v2 || v1 != null && v1.equals(v2))) {
+        res.remove(key);
       }
     }
     return res;
@@ -618,10 +621,8 @@ public class ContainerUtil extends ContainerUtilRt {
   @NotNull
   @Contract(pure=true)
   public static <K, V> Map<K,Couple<V>> diff(@NotNull Map<? extends K, ? extends V> map1, @NotNull Map<? extends K, ? extends V> map2) {
-    final Set<K> keys = new HashSet<K>();
-    keys.addAll(map1.keySet());
-    keys.addAll(map2.keySet());
-    final Map<K, Couple<V>> res = new HashMap<K, Couple<V>>();
+    Set<K> keys = union(map1.keySet(), map2.keySet());
+    Map<K, Couple<V>> res = new HashMap<K, Couple<V>>();
     for (K k : keys) {
       V v1 = map1.get(k);
       V v2 = map2.get(k);