Question

完成任务我需要实现函数Change，它将取值并将其分成硬币列表中的可能组合（随机列表）例如：

DatePickerDialog.OnDateSetListener beginDate = new DatePickerDialog.OnDateSetListener() {
        @Override
        public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
            c.set(Calendar.YEAR,year);
            c.set(Calendar.MONTH,monthOfYear);
            c.set(Calendar.DAY_OF_MONTH,dayOfMonth);
            setBeginDateOnView();
        }
    };

 public void beginDateOnClick(View view) {
        new DatePickerDialog(CreateEventActivity.this,beginDate,c.get(Calendar.YEAR),c.get(Calendar.MONTH),c.get(Calendar.DAY_OF_MONTH)).show();
    }

  public void setBeginDateOnView() {
        String dateFormat = "dd-MM-yyyy";
        SimpleDateFormat sdf = new SimpleDateFormat(dateFormat, Locale.getDefault());
        edtBeginDate.setText(sdf.format(c.getTime()));

这就是我所做的：

coins = [2,3,7]
GHCi> change 7
[[2,2,3],[2,3,2],[3,2,2],[7]]

但这段代码很慢。帮助更快地完成此程序。作为工作的一部分，据说这项任务很容易在生成器列表和递归的帮助下完成。提前感谢您的帮助。

Answer 1

import Data.List

change :: [Int] -> Int -> [[Int]]
change _ 0 = []
change coins n = do
  x <- [c | c <- coins, c <= n]
  if x == n
    then return [x]
    else do
      xs <- change coins (n - x)
--    if (null xs)
--      then return [x]
--      else if x < (head xs)
--        then []
--        else return (x:xs)
      return (x:xs)

change' :: Int -> [[Int]]
change' = change [2,3,7]

test7 = change' 7
test6 = change' 6
test5 = change' 5
test4 = change' 4

Answer 2

您正在进行大量过滤，elem等等，并对数据类型施加了很多限制。将此视为一个动态问题，您经常需要弄清楚有多少种方式可以返回total金额的变化。

找到特定硬币的可能性后，您可以将其从列表中删除。

这是我提出的解决方案，包含在一个功能中。在列表理解中，请注意我为remaining变量赋值，并且这些值的范围为[0，total]，每x跳转，其中x是面额。例如，如果您必须计算$ 0.25总计$ 2的次数，那么该列表理解最终会： [countChange 2, countChange 1.75,countChange 1.5, countChange 1.25,...]，但countChange的下一次迭代也不包括0.25硬币 - 因为我们只是测试了＃34;这一点。

-- Amount to return -> List of Coin denominations available
countChange :: Integer -> [Integer] -> Integer
countChange _ [] = 0 -- No coins at all, so no change can be given
countChange 0 _ = 1 -- Only one way to return 0 change
countChange total (x:xs) = sum [countChange (total-remaining) xs | remaining <- [0,x..total]]

Answer 3

使用MemoCombinators。这很快！ PLS。尝试改变100

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

NSString *string1 = @"cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:string1];
    if(!cell)
    {

        cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:string1];
        UILabel *label1 = (UILabel*)[cell.contentView viewWithTag:401];
        CGFloat widthLabelHeader = CGRectGetWidth(orderTable.frame)/7;
        if(!label1)

        {

            label1 = [[UILabel alloc]init];
            label1.frame = CGRectMake(0, 0, widthLabelHeader, 45);
            label1.layer.borderWidth = 0.5;
            label1.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label1];
        }
               label1.textAlignment = NSTextAlignmentCenter;




        UILabel *label2 = (UILabel*)[cell.contentView viewWithTag:402];
        if(!label2)

        {

            label2 = [[UILabel alloc]init];
            label2.frame = CGRectMake(CGRectGetMaxX(label1.frame), 0, widthLabelHeader, 45);
            label2.layer.borderWidth = 0.5;
            label2.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label2];
        }
              label2.textAlignment = NSTextAlignmentCenter;


        UILabel *label3 = (UILabel*)[cell.contentView viewWithTag:403];
        if(!label3)

        {

            label3 = [[UILabel alloc]init];
            label3.frame = CGRectMake(CGRectGetMaxX(label2.frame), 0, widthLabelHeader, 45);
            label3.layer.borderWidth = 0.5;
            label3.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label3];
        }
        label3.textAlignment = NSTextAlignmentCenter;

        UILabel *label4 = (UILabel*)[cell.contentView viewWithTag:404];
        if(!label4)

        {
            label4 = [[UILabel alloc]init];
            label4.frame = CGRectMake(CGRectGetMaxX(label3.frame), 0, widthLabelHeader, 45);
            label4.layer.borderWidth = 0.5;
            label4.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label4];
        }
        label4.textAlignment = NSTextAlignmentCenter;

        UILabel *label5 = (UILabel*)[cell.contentView viewWithTag:405];
        if(!label5)

        {
            label5 = [[UILabel alloc]init];
            label5.frame = CGRectMake(CGRectGetMaxX(label4.frame), 0, widthLabelHeader, 45);
            label5.layer.borderWidth = 0.5;
            label5.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label5];
        }
        label5.textAlignment = NSTextAlignmentCenter;


        UILabel *label6 = (UILabel*)[cell.contentView viewWithTag:406];
        if(!label6)

        {
            label6 = [[UILabel alloc]init];
            label6.frame = CGRectMake(CGRectGetMaxX(label5.frame), 0, widthLabelHeader, 45);
            label6.layer.borderWidth = 0.5;
            label6.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label6];
        }
        label6.textAlignment = NSTextAlignmentCenter;


        UILabel *label7 = (UILabel*)[cell.contentView viewWithTag:407];
        if(!label7)

        {
            label7 = [[UILabel alloc]init];
            label7.frame = CGRectMake(CGRectGetMaxX(label6.frame), 0, widthLabelHeader, 45);
            label7.layer.borderWidth = 0.5;
            label7.font = [UIFont fontWithName:@"ChalkboardSE-Bold" size:14];
            [cell.contentView addSubview:label7];
        }
        label7.textAlignment = NSTextAlignmentCenter;




    dict1 = [array1 objectAtIndex:indexPath.row];
    if( dict1)
    {

        label1.text = [dict1 objectForKey:@"key1" ];
        label1.backgroundColor = [UIColor lightGrayColor];

        label2.text = [dict1 objectForKey:@"key2" ];
        label2.backgroundColor = [UIColor lightGrayColor];

        label3.text = [dict1 objectForKey:@"key3" ];
        label3.backgroundColor = [UIColor lightGrayColor];

        label4.text = [dict1 objectForKey:@"key4" ];
        label4.backgroundColor = [UIColor lightGrayColor];

        label5.text = [dict1 objectForKey:@"key5" ];
        label5.backgroundColor = [UIColor lightGrayColor];


        label6.text = [dict1 objectForKey:@"key6" ];
        label6.backgroundColor = [UIColor lightGrayColor];


        label7.text = [dict1 objectForKey:@"key7" ];
        label7.backgroundColor = [UIColor lightGrayColor];
    }}
    return cell;
    }

Haskell优化程序

3 个答案: