函数功能:传入一个数组，返回数组中第二大数已知数组中的对象都是数字构成的字符串，且任意两元素不相等 如传入：@[@"1",@"2",@"3",@"4"]，返回@"3"

- (Nsstring *)secondMaxItem:(NSArray *)ary
{
    int max=[ary[0] intValue];
    int secondmax=[ary[1] intValue];
     max=[ary[0] intValue]>[ary[1] intValue]?[ary[0] intValue]:[ary[1] intValue];
     secondmax=[ary[0] intValue]>[ary[1] intValue]?[ary[1] intValue]:[ary[0] intValue];
    for (NSUInteger i=2; i<=ary.count-1; i++)
    {
        if ([ary[i] intValue]>max)
        {
            secondmax=max;
            max=[ary[i] intValue];
        }
        else if([ary[i] intValue]>secondmax)
        {
            secondmax=[ary[i] intValue];
        }
    }
    return [Nsstring stringWithFormat:@"%d",secondmax];
    
}