說明

1. 這是一些iOS面試的小小算法題，在此做個筆記，以供參考和以后的翻閱拱绑。
2. 用C語言實(shí)現(xiàn)字符串的翻轉(zhuǎn)和計算一個View上的UIImageView的個數(shù)，這兩個算法題目丽蝎，只給出代碼猎拨，工程文件未做上傳，請諒解屠阻。
3. Demo是一個macOS的命令行工程红省，為了避免運(yùn)行模擬器的麻煩。
4. 某些代碼国觉，并未按照《禪與Objective-C編程藝術(shù)》中寫的那樣規(guī)范吧恃，請輕噴。
5. Demo地址

用C語言寫一個函數(shù)麻诀，實(shí)現(xiàn)翻轉(zhuǎn)字符串痕寓，并考慮時間復(fù)雜度傲醉、空間復(fù)雜度，盡可能最小

/*實(shí)現(xiàn)字符串翻轉(zhuǎn)*/
char *reverse_str(char *str) {
    if(NULL == str) { //字符串為空直接返回
        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) { //取地址呻率，交換兩個字符
        temp = *begin;
        *begin = *end;
        *end = temp;
        begin++;
        end--;
    }

    return str; //返回結(jié)果
}

void main() {
    char str[] = "kengdiedemianshiti";
    printf(reverse_str(str));
}

用Objective-C語言 實(shí)現(xiàn)冒泡排序

//Objective-C 冒泡排序
+ (void)inputNeedArray:(NSMutableArray *)array
{
    //依次拿相鄰的兩個元素做比較
    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語言 實(shí)現(xiàn)選擇排序

//Objective-C 選擇排序
+ (void)inputNeedArray:(NSMutableArray *)array
{
    //拿第一個跟后面的挨個比較
    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(@"------");
    }
}

寫一個函數(shù)硬毕，給它傳一個數(shù)組，去除數(shù)組中包含特定字符的元素礼仗，并返回一個新的數(shù)組

//輸入一個數(shù)組吐咳，返回去除包含"Foo"字符串的元素的一個數(shù)組
//[@"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);
  }

寫一個函數(shù)，將兩個有序數(shù)組合并后元践，得到一個新的有序數(shù)組韭脊，并且無重復(fù)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;
}

關(guān)于GCD的打印問題

+ (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]);
}

關(guān)于object_getClass 和 class的問題

#import <objc/runtime.h>

+ (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]);
}

寫一個函數(shù)，要求能計算出這個View上的子視圖中UIImageView的個數(shù)

- (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;
}

寫一個函數(shù)单旁，傳給它一個二維矩陣和一個數(shù)值涤垫，來判斷是否存在這樣的元素在矩陣中

+ (void)checkElementFromArray:(NSArray *)array findNumber:(int)number
{
    BOOL isOrNot = NO;
    //判斷二維數(shù)組是否為空
    if (array.count != 0) {
        //總行數(shù)
        int rows = (int)array.count;
        NSArray *arr = array[0];
        if (arr.count != 0) {
            //總列數(shù)
            int columns = (int)arr.count;
            //行
            int row = 0;
            //列
            int column = columns - 1; //最后一個元素
            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);
}