iOS - 任意两个类的公共父类

1.简单 for 循环

- (Class)commonClass1:(Class)classA andClass:(Class)classB {
    NSArray *arr1 = [self superClasses:classA];
    NSArray *arr2 = [self superClasses:classB];
    for (NSUInteger i = 0; i < arr1.count; ++i) {
        Class targetClass = arr1[i];
        for (NSUInteger j = 0; j < arr2.count; ++j) {
            if (targetClass == arr2[j]) {
                return targetClass;
            }
        }
    }
    return nil;
}
//获取所有父类
- (NSArray *)superClasses:(Class)cls{

    if (cls == nil) {
        return @[];
    }
    NSMutableArray *res = [NSMutableArray array];
    while (cls != nil) {
        [res addObject:cls];
        cls = [cls superclass];
    }
    return [res copy];
}

2.优化

iOS 的集成关系里：所有的类的终极父类：NSObject，且 iOS 是单继承.
其实就相当于这两个类的继承链从 NSObject 开始向下一直是重合的，直到最后的一个公共父类才开始分开，这个最后的公共父类也是最近的公共父类，这是典型的倒 Y 字型链表组合。

- (Class)commonSuperClsss:(Class)clsA withClssB:(Class )clsB{
        
    NSArray *clsAs = [[[self superClasses:[clsA class]] reverseObjectEnumerator] allObjects];
    NSArray *clsBs = [[[self superClasses:[clsB class]] reverseObjectEnumerator] allObjects];

    NSInteger count = clsAs.count > clsBs.count ? clsBs.count : clsAs.count;
    int idx = -1;
    for (int i = 0; i < count; i ++) {
        idx = i;
        if (clsAs[i] != clsBs[i]) {
            break;
        }
    }
    idx = idx == 0 ? 0 : idx - 1;
    return clsAs[idx];
}