IOS 數組去重及排序

NSArray *a1 = @[@"a",@"b",@"a",@"c",@"d"];

    

    NSSet *set = [NSSet setWithArray:a1];

    

    a1 = (NSArray *)set;

    

    NSArray *a2 = [a1 sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {

        NSString *aa = obj1;

        NSInteger asciia = [aa characterAtIndex:0];

        

        NSString *bb = obj2;

        NSInteger asciib = [bb characterAtIndex:0];

        

        if (asciia > asciib) {

            return (NSComparisonResult)NSOrderedDescending;

        }

        

        return (NSComparisonResult)NSOrderedSame;

    }];

    

    NSLog(@"%@",a2); 

結果

2015-08-18 16:24:48.523 T123[4600:194933] (

    a,

    b,

    c,

    d

)