iOS 数组集合（交集，并集，差集，子集）

NSArray *array1 = @[@"11",@"22",@"33"];
NSArray *array2 = @[@"11",@"55",@"66"];
NSMutableSet *set1 = [NSMutableSet setWithArray:array1];
NSMutableSet *set2 = [NSMutableSet setWithArray:array2];

[set1 unionSet:set2]; //取并集后 set1中为11，22，33，55，66
[set1 intersectSet:set2]; //取交集后 set1中为11
[set1 minusSet:set2]; //取差集后 set1中为22，33，55，66