基础算法题

1. 字符串翻转

-(void)test2{
    NSString *str = @"hello world";
    NSArray *array = [str componentsSeparatedByString:@" "];
    
    NSMutableString *dstStr = [NSMutableString string];
    for (NSInteger idx = array.count - 1; idx >= 0 ; idx--) {
        [dstStr appendFormat:@"%@ ",array[idx]];
    }
    NSLog(@"%@",dstStr);
}

2. 数组中第二大的数字

-(void)test3{
    NSArray *array = @[@(1),@(51),@(11),@(0)];
    
    array = [array sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
        return [(NSNumber *)obj1 integerValue] <= [(NSNumber *)obj2 integerValue];
    }];
    
    NSLog(@"%@",array);
    if (array.count >= 2) {
        NSLog(@"第二大的数字为:%@",array[1]);
    }
}