生成100个 "20180520" 这样的时间字符串 写入txt文件

主要想记录一下
1 . 写NSString 到txt 
2. 数组的去重
3. 数组的截取
4. 数组分割

代码如下：

NSString *year = @"2018";

    NSArray *momth = @[@"05",@"06",@"07",@"08",@"09",@"10",@"11",@"12"];

    NSArray *day = @[@"01",@"02",@"03",@"04",@"05",@"06",@"07",@"08",@"09",@"10",@"11",@"12",@"13",@"14",@"15",@"16",@"17",@"18",@"19",@"20",@"21",@"22",@"23",@"24",@"25",@"26",@"27",@"28",@"29",@"30",@"31"];

    NSMutableArray *dateStrArr = [NSMutableArray array];

    for (int i = 0 ; i < 200; i++) {

        NSString *momthStr = momth[arc4random()%momth.count];

        NSString *dayStr = day[arc4random()%day.count];

        if ([momthStr isEqualToString:@"02"] && [dayStr integerValue] > 28) {

            continue;

        }

        //NSLog(@"%@%@%@",year,momthStr,dayStr);

        NSString *dateStr = [NSString stringWithFormat:@"%@%@%@",year,momthStr,dayStr];

        [dateStrArr addObject:dateStr];

        //dateStr = [NSString stringWithFormat:@" %@",dateStr];

    }

    //去重

    NSArray *result = [dateStrArr valueForKeyPath:@"@distinctUnionOfObjects.self"];

    NSLog(@"去重1之后 =  %d",result.count);

    //选100个

    NSArray *finalArr = [result subarrayWithRange:NSMakeRange(0, 100)];

    NSLog(@"去重1之后 =  %d",finalArr.count);

    NSString *final = [finalArr componentsJoinedByString:@" "];

    //NSLog(@"%@",final);

    //NSFileHandle文件

    //1.创建文件

    NSFileManager *fm = [NSFileManager defaultManager];

    //NSString *str = @"this is a test. 666";

    NSData *data = [final dataUsingEncoding:NSUTF8StringEncoding];

    [fm createFileAtPath:@"/Users/liuwei/Desktop/date2.txt" contents:data attributes:nil];