iOS常见算法以及应用知识点总结

#pragma mark - Objective-C
//冒泡排序
- (void)bubbleSort:(id)array{
  if (!([array isKindOfClass:[NSArray class]] || [array isKindOfClass:[NSMutableArray class]])) {
    NSLog(@"传入的参数不是数组类型");
    return;
  }
  NSMutableArray *tmpArr;
  if ([array isKindOfClass:[NSMutableArray class]]) {
    tmpArr = array;
  }else{
    tmpArr = [array mutableCopy];
  }
  for (int i = 0; i<tmpArr.count; i++) {
    for (int j = 0; j < tmpArr.count -1; j++) {
      if ([tmpArr[j] compare:tmpArr[j+1]] == NSOrderedDescending) {
        [tmpArr exchangeObjectAtIndex:i withObjectAtIndex:j+1];
      }
    }
  }
  NSLog(@"排序完的结果为:%@/n",tmpArr);
}

#pragma mark - C
//冒泡排序
void bubble_sort(int arr[], const int size){
  for (int i = 0; i < size; i++) {
    for (int j = 0; j<size -1 ; j++) {
      if (arr[j] > arr[j+1]) {
        swap(arr[j], arr[j+1]);
      }
    }
  }
}

void swap(int i,int j){
  i = i + j;
  j = i - j;
  i = i - j;
}

- (void)quickSort:(NSMutableArray*)array low:(int)low high:(int)high{
  
  if (array == nil || array.count == 0) {
    return;
  }
  if (low >= high) {
    return;
  }
  //取中值
  int middle = low + (high - low)/2;
  NSNumber *prmt = array[middle];
  int i = low;
  int j = high;
  
   //开始排序，使得left<prmt 同时right>prmt
  while (i <= j) {
//    while ([array[i] compare:prmt] == NSOrderedAscending) {
//      i++;
//    }
    while ([array[i] intValue] < [prmt intValue]) {
      i++;
    }
//    while ([array[j] compare:prmt] == NSOrderedDescending)
    while ([array[j] intValue] > [prmt intValue]) {
      j--;
    }
    
    if(i <= j){
      [array exchangeObjectAtIndex:i withObjectAtIndex:j];
      i++;
      j--;
    }
  }
  
  if (low < j) {
    [self quickSort:array low:low high:j];
  }
  if (high > i) {
    [self quickSort:array low:i high:high];
  }
}

//快速排序
int a[101],n;//定义全局变量，这两个变量需要在子函数中使用
void quicksort(int left,int right)
{
  int i,j,t,temp;
  if(left>right)
    return;
  
  temp=a[left]; //temp中存的就是基准数
  i=left;
  j=right;
  while(i!=j){
    //顺序很重要，要先从右边开始找
    while(a[j]>=temp && i<j)
      j--;
    //再找右边的
    while(a[i]<=temp && i<j)
      i++;
    //交换两个数在数组中的位置
    if(i<j){
      t=a[i];
      a[i]=a[j];
      a[j]=t;
    }
  }
  //最终将基准数归位
  a[left]=a[i];
  a[i]=temp;
  
  quicksort(left,i-1);//继续处理左边的，这里是一个递归的过程
  quicksort(i+1,right);//继续处理右边的 ，这里是一个递归的过程
}

- (void)selectSort:(NSMutableArray *)array
{
  if(array == nil || array.count == 0){
    return;
  }
  
  int min_index;
  for (int i = 0; i < array.count; i++) {
    min_index = i;
    for (int j = i + 1; j<array.count; j++) {
      if ([array[j] compare:array[min_index]] == NSOrderedAscending) {
        [array exchangeObjectAtIndex:j withObjectAtIndex:min_index];
      }
    }
  }
}

- (void)inserSort:(NSMutableArray *)array
{
  if(array == nil || array.count == 0){
    return;
  }
  
  for (int i = 0; i < array.count; i++) {
    NSNumber *temp = array[i];
    int j = i-1;
    
    while (j >= 0 && [array[j] compare:temp] == NSOrderedDescending) {
      [array replaceObjectAtIndex:j+1 withObject:array[j]];
      j--;
    }
    
    [array replaceObjectAtIndex:j+1 withObject:temp];
  }
}

//希尔排序,初始的dk值为array.count/2
- (void)shellSort:(NSMutableArray *)array dk:(int)dk
{
  
  if(array == nil || array.count == 0||dk>=array.count){
    return;
  }
  
  for (int i = 0; i < array.count; i ++) {
    NSNumber *temp = array[i];
    int j = i - dk;
    
      //若第i个元素大于i-1元素，直接插入。小于的话，移动有序表后插入
      while (j >= 0 && [array[j] compare:temp] == NSOrderedDescending) {
        [array replaceObjectAtIndex:j+dk withObject:array[j]];
        j-=dk;
      }
      [array replaceObjectAtIndex:j+dk withObject:temp];
    
  }
  
  while (dk>=1) {
    dk = dk/2;
    [self ShellSort:array dk:dk];
  }
}

+(NSData *)compressImage:(UIImage *)image toByte:(NSUInteger)maxLength
{
  // Compress by quality
  CGFloat compression = 1;
  NSData *data = UIImageJPEGRepresentation(image, compression);
  if (data.length < maxLength) return data;
  //采用二分法提高性能
  CGFloat max = 1;
  CGFloat min = 0;
  for (int i = 0; i < 6; ++i) {
    compression = (max + min) / 2;
    data = UIImageJPEGRepresentation(image, compression);
    if (data.length < maxLength * 0.9) {
      min = compression;
    } else if (data.length > maxLength) {
      max = compression;
    } else {
      break;
    }
  }
  UIImage *resultImage = [UIImage imageWithData:data];
  if (data.length < maxLength) return data;
  
  // Compress by size
  NSUInteger lastDataLength = 0;
  while (data.length > maxLength && data.length != lastDataLength) {
    lastDataLength = data.length;
    CGFloat ratio = (CGFloat)maxLength / data.length;
    CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),
                 (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank
    UIGraphicsBeginImageContext(size);
    [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
    resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    data = UIImageJPEGRepresentation(resultImage, compression);
  }
  
  return data;
}

+(NSData *)compressImage:(UIImage *)image
{
  NSData *data=UIImageJPEGRepresentation(image, 1.0);
  if (data.length>300*1024) {
    
    if (data.length>1024*1024) {//1M以及以上
      
      data=UIImageJPEGRepresentation(image, 0.5);
      
    }else if (data.length>300*1024) {//0.5M-1M
      
      data=UIImageJPEGRepresentation(image, 0.8);
      
    }
  }
  return data;
}