iOS算法小记

• 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。
  5. Demo地址

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• 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));
  }
  
  
  

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• 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(@"------");
      }
  }
  

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• 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);
    }
  

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• 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;
  }
  

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• 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]);
  }
  

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• 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;
  }
  

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• 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);
  }
  

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