Add LCS diffing support to NSArray

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -475,6 +475,8 @@
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+		DBC452DB1C5BF64600B16017 /* NSArray+Diffing.h in Headers */ = {isa = PBXBuildFile; fileRef = DBC452D91C5BF64600B16017 /* NSArray+Diffing.h */; };
+		DBC452DC1C5BF64600B16017 /* NSArray+Diffing.m in Sources */ = {isa = PBXBuildFile; fileRef = DBC452DA1C5BF64600B16017 /* NSArray+Diffing.m */; };
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@@ -802,6 +804,8 @@
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+		DBC452D91C5BF64600B16017 /* NSArray+Diffing.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSArray+Diffing.h"; sourceTree = "<group>"; };
+		DBC452DA1C5BF64600B16017 /* NSArray+Diffing.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSArray+Diffing.m"; sourceTree = "<group>"; };
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@@ -1164,6 +1168,8 @@
 				0442850C1BAA64EC00D16268 /* ASMultidimensionalArrayUtils.mm */,
 				AEB7B0181C5962EA00662EF4 /* ASDefaultPlayButton.h */,
 				AEB7B0191C5962EA00662EF4 /* ASDefaultPlayButton.m */,
+				DBC452D91C5BF64600B16017 /* NSArray+Diffing.h */,
+				DBC452DA1C5BF64600B16017 /* NSArray+Diffing.m */,
 			);
 			path = Private;
 			sourceTree = "<group>";
@@ -1354,6 +1360,7 @@
 				ACF6ED201B17843500DA7C62 /* ASDimension.h in Headers */,
 				058D0A78195D05F900B7D73C /* ASDisplayNode+DebugTiming.h in Headers */,
 				DECBD6E71BE56E1900CF4905 /* ASButtonNode.h in Headers */,
+				DBC452DB1C5BF64600B16017 /* NSArray+Diffing.h in Headers */,
 				058D0A4C195D05CB00B7D73C /* ASDisplayNode+Subclasses.h in Headers */,
 				258FF4271C0D152600A83844 /* ASRangeHandlerVisible.h in Headers */,
 				058D0A4A195D05CB00B7D73C /* ASDisplayNode.h in Headers */,
@@ -1782,6 +1789,7 @@
 				ACF6ED1D1B17843500DA7C62 /* ASCenterLayoutSpec.mm in Sources */,
 				18C2ED801B9B7DE800F627B3 /* ASCollectionNode.mm in Sources */,
 				92DD2FE41BF4B97E0074C9DD /* ASMapNode.mm in Sources */,
+				DBC452DC1C5BF64600B16017 /* NSArray+Diffing.m in Sources */,
 				AC3C4A521A1139C100143C57 /* ASCollectionView.mm in Sources */,
 				205F0E1E1B373A2C007741D0 /* ASCollectionViewLayoutController.mm in Sources */,
 				058D0A13195D050800B7D73C /* ASControlNode.m in Sources */,

AsyncDisplayKit/Private/NSArray+Diffing.h

@@ -0,0 +1,18 @@
+//
+//  NSArray+Diffing.h
+//  AsyncDisplayKit
+//
+//  Created by Levi McCallum on 1/29/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface NSArray (Diffing)
+
+/**
+ * Uses a bottom-up memoized longest common subsequence solution to identify differences. Runs in O(mn) complexity.
+ */
+- (void)asdk_diffWithArray:(NSArray *)array insertions:(NSMutableIndexSet **)insertions deletions:(NSMutableIndexSet **)deletions;
+
+@end

AsyncDisplayKit/Private/NSArray+Diffing.m

@@ -0,0 +1,67 @@
+//
+//  NSArray+Diffing.m
+//  AsyncDisplayKit
+//
+//  Created by Levi McCallum on 1/29/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import "NSArray+Diffing.h"
+
+@implementation NSArray (Diffing)
+
+- (void)asdk_diffWithArray:(NSArray *)array insertions:(NSMutableIndexSet **)insertions deletions:(NSMutableIndexSet **)deletions
+{
+  NSIndexSet *commonIndexes = [self _asdk_commonIndexesWithArray:array];
+  
+  if (insertions) {
+    NSArray *commonObjects = [self objectsAtIndexes:commonIndexes];
+    for (NSInteger i = 0, j = 0; i < commonObjects.count || j < array.count;) {
+      if (i < commonObjects.count && j < array.count && [commonObjects[i] isEqual:array[j]]) {
+        i++; j++;
+      } else {
+        [*insertions addIndex:j];
+        j++;
+      }
+    }
+  }
+  
+  if (deletions) {
+    for (NSInteger i = 0; i < self.count; i++) {
+      if (![commonIndexes containsIndex:i]) {
+        [*deletions addIndex:i];
+      }
+    }
+  }
+}
+
+- (NSIndexSet *)_asdk_commonIndexesWithArray:(NSArray *)array
+{
+  NSInteger lengths[self.count+1][array.count+1];
+  for (NSInteger i = self.count; i >= 0; i--) {
+    for (NSInteger j = array.count; j >= 0; j--) {
+      if (i == self.count || j == array.count) {
+        lengths[i][j] = 0;
+      } else if ([self[i] isEqual:array[j]]) {
+        lengths[i][j] = 1 + lengths[i+1][j+1];
+      } else {
+        lengths[i][j] = MAX(lengths[i+1][j], lengths[i][j+1]);
+      }
+    }
+  }
+  
+  NSMutableIndexSet *common = [NSMutableIndexSet indexSet];
+  for (NSInteger i = 0, j = 0; i < self.count && j < array.count;) {
+    if ([self[i] isEqual:array[j]]) {
+      [common addIndex:i];
+      i++; j++;
+    } else if (lengths[i+1][j] >= lengths[i][j+1]) {
+      i++;
+    } else {
+      j++;
+    }
+  }
+  return common;
+}
+
+@end