如何在NSArray中找到NSNumbers的中值？

[array valueForKeyPath:@"@median.self"];

NSMethodSignature *signature = [array methodSignatureForSelector:@selector(median)];
NSInteger median = [signature median];

@implementation NSNumber (Median)

- (double)median {
    NSUInteger count = [self count];
    if (count == 0) {
        return 0;
    }
    NSUInteger middle = count / 2;
    NSUInteger lower = 0;
    NSUInteger upper = count - 1;
    while (lower < upper) {
        NSUInteger mid = (lower + upper) / 2;
        NSUInteger countMid = [self countBetween:lower and:mid];
        NSUInteger countHigher = [self countBetween:mid and:upper];
        if (countMid < countHigher) {
            lower = mid + 1;
        } else {
            upper = mid;
        }
    }
    return (double)lower + (double)count / 2;
}

@end

NSNumber *medianNumber = [array median];
double median = [medianNumber doubleValue];