说明

1. 这是一些iOS面试的小小算法题，在此做个笔记，以供参考和以后的翻阅。
2. 用C语言实现字符串的翻转和计算一个View上的UIImageView的个数，这两个算法题目，只给出代码，工程文件未做上传，请谅解。
3. Demo是一个macOS的命令行工程，为了避免运行模拟器的麻烦。
4. 某些代码，并未按照《禅与Objective-C编程艺术》中写的那样规范，请轻喷。

用C语言写一个函数，实现翻转字符串，并考虑时间复杂度、空间复杂度，尽可能最小

/*实现字符串翻转*/char *reverse_str(char *str) {    if(NULL == str) { //字符串为空直接返回        return str;    }    char *begin;    char *end;    begin = end = str;    while(*end != '\0') { //end指向字符串的末尾        end++;    }    --end;    char temp;    while(begin < end) { //取地址，交换两个字符        temp = *begin;        *begin = *end;        *end = temp;        begin++;        end--;    }    return str; //返回结果}void main() {    char str[] = "kengdiedemianshiti";    printf(reverse_str(str));}

用Objective-C语言 实现冒泡排序

//Objective-C 冒泡排序+ (void)inputNeedArray:(NSMutableArray *)array{    //依次拿相邻的两个元素做比较    for (int i = 0; i < array.count; ++i) {        for (int j = 0; j < array.count - 1; ++j) {            if (array[j] < array[j + 1]) {                [array exchangeObjectAtIndex:j withObjectAtIndex:j + 1];            }            NSString * str = @"";            for (NSNumber * value in array) {                str = [str stringByAppendingString:[NSString stringWithFormat:@"%zd ",[value integerValue]]];            }            NSLog(@"%@",str);        }        NSLog(@"------");    }}

用Objective-C语言 实现选择排序

//Objective-C 选择排序+ (void)inputNeedArray:(NSMutableArray *)array{    //拿第一个跟后面的挨个比较    for (int i = 0; i < array.count; i++) {        for (int j = i + 1; j < array.count; j++) {            if (array[i] < array[j]) {                [array exchangeObjectAtIndex:i withObjectAtIndex:j];            }                        NSString * str = @"";            for (NSNumber * value in array) {                str = [str stringByAppendingString:[NSString stringWithFormat:@"%zd ",[value integerValue]]];            }            NSLog(@"%@",str);        }        NSLog(@"------");    }}

写一个函数，给它传一个数组，去除数组中包含特定字符的元素，并返回一个新的数组

//输入一个数组，返回去除包含"Foo"字符串的元素的一个数组//[@"A", @"FooB", @"C", @"FooH", @"FooI"+ (void)returnNeedArray:(NSMutableArray *)array  {    NSMutableArray *muArr = [NSMutableArray arrayWithCapacity:1];    for (int i = 0; i < array.count; i++) {        if (![array[i] hasPrefix:@"Foo"]) {            [muArr addObject:array[i]];        }    }    NSLog(@"%@", muArr);  }

写一个函数，将两个有序数组合并后，得到一个新的有序数组，并且无重复元素

+ (NSMutableArray *)combineArray:(NSArray *)arrayNumberOne otherArray:(NSArray *)arrayNumberTwo{    //    NSArray *array1 = @[@1, @3, @5, @6,];    //    NSArray *array2 = @[@2, @3, @4, @5, @7];    NSMutableArray *resultArray = [NSMutableArray arrayWithCapacity:1];    int i = 0;    int j = 0;    while (i < arrayNumberOne.count && j < arrayNumberTwo.count) {        if (arrayNumberOne[i] < arrayNumberTwo[j]) {            resultArray[i + j] = arrayNumberOne[i];            i++;        }        else {            resultArray[i + j] = arrayNumberTwo[j];            j++;        }    }    while (i < arrayNumberOne.count) {        resultArray[i + j] = arrayNumberOne[i];        i++;    }    while (j < arrayNumberTwo.count) {        resultArray[i + j] = arrayNumberTwo[j];        j++;    }    //去重 有序    NSOrderedSet *set = [NSMutableOrderedSet orderedSetWithArray:resultArray];    NSLog(@"%@", set.array);    return resultArray;}

关于GCD的打印问题

+ (void)prinfLogForGCD{    dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);    NSLog(@"1 --- %@", [NSThread currentThread]);    dispatch_async(queue, ^{        NSLog(@"2 --- %@", [NSThread currentThread]);        dispatch_sync(queue, ^{            NSLog(@"3 --- %@", [NSThread currentThread]);        });        NSLog(@"4 --- %@", [NSThread currentThread]);    });    NSLog(@"5 --- %@", [NSThread currentThread]);}

关于object_getClass 和 class的问题

#import 
       
        + (void)printLogForObjcgetClassAndClass{    XXPrintObjectClass *obj = [XXPrintObjectClass new];        NSLog(@"instance         :%p", obj);    NSLog(@"class            :%p", object_getClass(obj));    NSLog(@"meta class       :%p", object_getClass(object_getClass(obj)));    NSLog(@"root meta        :%p", object_getClass(object_getClass(object_getClass(obj))));    NSLog(@"root meta's meta :%p", object_getClass(object_getClass(object_getClass(object_getClass(obj)))));        NSLog(@"---------------------------------------------");        NSLog(@"class            :%p", [obj class]);    NSLog(@"meta class       :%p", [[obj class] class]);    NSLog(@"root meta        :%p", [[[obj class] class] class]);    NSLog(@"root meta's meta :%p", [[[[obj class] class] class] class]);}
       

写一个函数，要求能计算出这个View上的子视图中UIImageView的个数

- (NSInteger)returnUIImageViewNumber:(UIView *)view{    static NSInteger a = 0;    for (int i = 0; i < view.subviews.count; i++) {        if ([[NSString stringWithFormat:@"%@", [view.subviews[i] class]] isEqualToString:@"UIImageView"]) {            a++;        }        else if (view.subviews[i].subviews.count != 0) {            [self returnUIImageViewNumber:view.subviews[i]];        }    }//    NSLog(@"%d", a);    return a;}

写一个函数，传给它一个二维矩阵和一个数值，来判断是否存在这样的元素在矩阵中

+ (void)checkElementFromArray:(NSArray *)array findNumber:(int)number{    BOOL isOrNot = NO;    //判断二维数组是否为空    if (array.count != 0) {        //总行数        int rows = (int)array.count;        NSArray *arr = array[0];        if (arr.count != 0) {            //总列数            int columns = (int)arr.count;            //行            int row = 0;            //列            int column = columns - 1; //最后一个元素            while (row < rows && column >= 0) {                NSString *arrStr = [NSString stringWithFormat:@"%@", array[row][column]];                NSString *numStr = [NSString stringWithFormat:@"%d", number];                int arrNumber = [arrStr intValue];                int targetNumber = [numStr intValue];                if (arrNumber == targetNumber) {                    isOrNot = YES;                    break;                }                else if (arrNumber > targetNumber) {                    --column;                }                else {                    ++row;                }            }        }    }    NSLog(@"%hhd", isOrNot);}