iOS 学习

1.快速排序

原理:

1. 先从数列中取出一个数作为基数
2. 分区过程,将比这个数大的数全放到它的右边,小于或等于它的数全放到它的左边
3. 再对左右区间重复第二步,直到各区间只有一个数;对两侧元素递归排序 

- (NSArray *)quickSort:(NSMutableArray *)dataArray {
    NSMutableArray *lessArray = [NSMutableArray array];
    NSMutableArray *bigArray  = [NSMutableArray array];
    if (dataArray.count < 1) {
        return dataArray;
    }
    int midNumber = arc4random() % [dataArray count];
    NSNumber *midValue = dataArray[midNumber];
    [dataArray removeObjectAtIndex:midNumber];
    for (NSNumber *number in dataArray) {
        if (number < midValue) {
            [lessArray addObject:number];
        }else{
            [bigArray addObject:number];
        }
    }
    NSMutableArray *tempArray = [NSMutableArray array];
    [tempArray addObjectsFromArray:[self quickSort:lessArray]];
    [tempArray addObject:midValue];
    [tempArray addObjectsFromArray:[self quickSort:bigArray]];
    return tempArray;
}

优化:从并发执行入手提升速度,利用 dispatch_apply 快速迭代器加速循环速度

#pragma mark - 优化
- (NSArray *)optimizeQuickSort:(NSMutableArray *)dataArray {
    NSMutableArray *lessArray = [NSMutableArray array];
    NSMutableArray *bigArray  = [NSMutableArray array];
    if (dataArray.count < 1) {
        return dataArray;
    }
    int midNumber = arc4random() % [dataArray count];
    NSNumber *midValue = dataArray[midNumber];
    [dataArray removeObjectAtIndex:midNumber];
    
    dispatch_queue_t concurrentQueue = dispatch_queue_create("com.cc.quickqeueue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_apply(dataArray.count, concurrentQueue, ^(size_t i) {
        int index = (int)i;
        NSNumber *num = dataArray[index];
        if (num < midValue) {
            [lessArray addObject:num];
        }else{
            [bigArray addObject:num];
        }
    });
    NSMutableArray *tempArray = [NSMutableArray array];
    [tempArray addObjectsFromArray:[self quickSort:lessArray]];
    [tempArray addObject:midValue];
    [tempArray addObjectsFromArray:[self quickSort:bigArray]];
    return tempArray;
}

2.冒泡算法

越小的元素会经由交换慢慢"浮"到数列的顶端

#pragma mark - 冒泡
- (void)bubble:(NSMutableArray *)dataArray {
    id temp;
    for (int i = 0; i < dataArray.count; i++) {
        for (int j = 0; j < dataArray.count; j++) {
            if (dataArray[i] > dataArray[j]) {
                temp = dataArray[i];
                dataArray[i] = dataArray[j];
                dataArray[j] = temp;
            }
        }
    }
    NSLog(@"%@",dataArray);
}