我有一个nxm个由非负整数组成的矩阵。例如:
2 3 4 7 1
1 5 2 6 2
4 3 4 2 1
2 1 2 4 1
3 1 3 4 1
2 1 4 3 2
6 9 1 6 4
“投下炸弹”会使目标细胞及其所有八个邻居的数量减少一个，直到最小值为零。
x x x
x X x
x x x
什么样的算法可以确定将所有细胞减少到零所需的最少炸弹数量?
B选项(因为我不是一个细心的读者)
事实上，问题的第一个版本并不是我要寻找的答案。我没有仔细阅读整个任务，有额外的约束条件，让我们说:
那么简单的问题是，当行中的序列必须是非递增的:
8 7 6 6 5是可能的输入序列
7 8 5 5 2是不可能的，因为7 -> 8在一个序列中增长。
也许为“简单”的问题找到答案会有助于为更难的问题找到解决方案。
PS:我相信当我们有几个相同的情况需要最少的炸弹来清除上面的线时，我们会选择在“左侧”使用最多炸弹的一个。还有什么证据是正确的吗?
当前回答
我也有28招。我使用了两个测试来确定最佳下一步:第一个是产生最小棋盘和的一步。其次，对于相等的和，产生最大密度的移动，定义为:
number-of-zeros / number-of-groups-of-zeros
我是哈斯克尔。“解决板”显示引擎的解决方案。你可以通过输入“main”来玩游戏，然后输入目标点，“best”作为推荐，或者“quit”退出。
输出: *主>解决板 [(4, 4),(3、6),(3),(2,2),(2,2),(4、6)(4、6),(2,6),(2),(4,2)(2,6),(3),(4,3)(2,6)(4,2)(4、6)(4、6),(3、6),(2,6)(2,6)(2、4)(2、4)(2,6),(6),(4,2)(4,2)(4,2)(4,2)]
import Data.List
import Data.List.Split
import Data.Ord
import Data.Function(on)
board = [2,3,4,7,1,
1,5,2,6,2,
4,3,4,2,1,
2,1,2,4,1,
3,1,3,4,1,
2,1,4,3,2,
6,9,1,6,4]
n = 5
m = 7
updateBoard board pt =
let x = fst pt
y = snd pt
precedingLines = replicate ((y-2) * n) 0
bomb = concat $ replicate (if y == 1
then 2
else min 3 (m+2-y)) (replicate (x-2) 0
++ (if x == 1
then [1,1]
else replicate (min 3 (n+2-x)) 1)
++ replicate (n-(x+1)) 0)
in zipWith (\a b -> max 0 (a-b)) board (precedingLines ++ bomb ++ repeat 0)
showBoard board =
let top = " " ++ (concat $ map (\x -> show x ++ ".") [1..n]) ++ "\n"
chunks = chunksOf n board
in putStrLn (top ++ showBoard' chunks "" 1)
where showBoard' [] str count = str
showBoard' (x:xs) str count =
showBoard' xs (str ++ show count ++ "." ++ show x ++ "\n") (count+1)
instances _ [] = 0
instances x (y:ys)
| x == y = 1 + instances x ys
| otherwise = instances x ys
density a =
let numZeros = instances 0 a
groupsOfZeros = filter (\x -> head x == 0) (group a)
in if null groupsOfZeros then 0 else numZeros / fromIntegral (length groupsOfZeros)
boardDensity board = sum (map density (chunksOf n board))
moves = [(a,b) | a <- [2..n-1], b <- [2..m-1]]
bestMove board =
let lowestSumMoves = take 1 $ groupBy ((==) `on` snd)
$ sortBy (comparing snd) (map (\x -> (x, sum $ updateBoard board x)) (moves))
in if null lowestSumMoves
then (0,0)
else let lowestSumMoves' = map (\x -> fst x) (head lowestSumMoves)
in fst $ head $ reverse $ sortBy (comparing snd)
(map (\x -> (x, boardDensity $ updateBoard board x)) (lowestSumMoves'))
solve board = solve' board [] where
solve' board result
| sum board == 0 = result
| otherwise =
let best = bestMove board
in solve' (updateBoard board best) (result ++ [best])
main :: IO ()
main = mainLoop board where
mainLoop board = do
putStrLn ""
showBoard board
putStr "Pt: "
a <- getLine
case a of
"quit" -> do putStrLn ""
return ()
"best" -> do putStrLn (show $ bestMove board)
mainLoop board
otherwise -> let ws = splitOn "," a
pt = (read (head ws), read (last ws))
in do mainLoop (updateBoard board pt)
其他回答
我想不出一个计算实际数字的方法除非用我最好的启发式方法计算轰炸行动并希望得到一个合理的结果。
So my method is to compute a bombing efficiency metric for each cell, bomb the cell with the highest value, .... iterate the process until I've flattened everything. Some have advocated using simple potential damage (i.e. score from 0 to 9) as a metric, but that falls short by pounding high value cells and not making use of damage overlap. I'd calculate cell value - sum of all neighbouring cells, reset any positive to 0 and use the absolute value of anything negative. Intuitively this metric should make a selection that help maximise damage overlap on cells with high counts instead of pounding those directly.
下面的代码在28个炸弹中达到了测试场的完全破坏(注意，使用潜在伤害作为度量，结果是31!)
using System;
using System.Collections.Generic;
using System.Linq;
namespace StackOverflow
{
internal class Program
{
// store the battle field as flat array + dimensions
private static int _width = 5;
private static int _length = 7;
private static int[] _field = new int[] {
2, 3, 4, 7, 1,
1, 5, 2, 6, 2,
4, 3, 4, 2, 1,
2, 1, 2, 4, 1,
3, 1, 3, 4, 1,
2, 1, 4, 3, 2,
6, 9, 1, 6, 4
};
// this will store the devastation metric
private static int[] _metric;
// do the work
private static void Main(string[] args)
{
int count = 0;
while (_field.Sum() > 0)
{
Console.Out.WriteLine("Round {0}:", ++count);
GetBlastPotential();
int cell_to_bomb = FindBestBombingSite();
PrintField(cell_to_bomb);
Bomb(cell_to_bomb);
}
Console.Out.WriteLine("Done in {0} rounds", count);
}
// convert 2D position to 1D index
private static int Get1DCoord(int x, int y)
{
if ((x < 0) || (y < 0) || (x >= _width) || (y >= _length)) return -1;
else
{
return (y * _width) + x;
}
}
// Convert 1D index to 2D position
private static void Get2DCoord(int n, out int x, out int y)
{
if ((n < 0) || (n >= _field.Length))
{
x = -1;
y = -1;
}
else
{
x = n % _width;
y = n / _width;
}
}
// Compute a list of 1D indices for a cell neighbours
private static List<int> GetNeighbours(int cell)
{
List<int> neighbours = new List<int>();
int x, y;
Get2DCoord(cell, out x, out y);
if ((x >= 0) && (y >= 0))
{
List<int> tmp = new List<int>();
tmp.Add(Get1DCoord(x - 1, y - 1));
tmp.Add(Get1DCoord(x - 1, y));
tmp.Add(Get1DCoord(x - 1, y + 1));
tmp.Add(Get1DCoord(x, y - 1));
tmp.Add(Get1DCoord(x, y + 1));
tmp.Add(Get1DCoord(x + 1, y - 1));
tmp.Add(Get1DCoord(x + 1, y));
tmp.Add(Get1DCoord(x + 1, y + 1));
// eliminate invalid coords - i.e. stuff past the edges
foreach (int c in tmp) if (c >= 0) neighbours.Add(c);
}
return neighbours;
}
// Compute the devastation metric for each cell
// Represent the Value of the cell minus the sum of all its neighbours
private static void GetBlastPotential()
{
_metric = new int[_field.Length];
for (int i = 0; i < _field.Length; i++)
{
_metric[i] = _field[i];
List<int> neighbours = GetNeighbours(i);
if (neighbours != null)
{
foreach (int j in neighbours) _metric[i] -= _field[j];
}
}
for (int i = 0; i < _metric.Length; i++)
{
_metric[i] = (_metric[i] < 0) ? Math.Abs(_metric[i]) : 0;
}
}
//// Compute the simple expected damage a bomb would score
//private static void GetBlastPotential()
//{
// _metric = new int[_field.Length];
// for (int i = 0; i < _field.Length; i++)
// {
// _metric[i] = (_field[i] > 0) ? 1 : 0;
// List<int> neighbours = GetNeighbours(i);
// if (neighbours != null)
// {
// foreach (int j in neighbours) _metric[i] += (_field[j] > 0) ? 1 : 0;
// }
// }
//}
// Update the battle field upon dropping a bomb
private static void Bomb(int cell)
{
List<int> neighbours = GetNeighbours(cell);
foreach (int i in neighbours)
{
if (_field[i] > 0) _field[i]--;
}
}
// Find the best bombing site - just return index of local maxima
private static int FindBestBombingSite()
{
int max_idx = 0;
int max_val = int.MinValue;
for (int i = 0; i < _metric.Length; i++)
{
if (_metric[i] > max_val)
{
max_val = _metric[i];
max_idx = i;
}
}
return max_idx;
}
// Display the battle field on the console
private static void PrintField(int cell)
{
for (int x = 0; x < _width; x++)
{
for (int y = 0; y < _length; y++)
{
int c = Get1DCoord(x, y);
if (c == cell)
Console.Out.Write(string.Format("[{0}]", _field[c]).PadLeft(4));
else
Console.Out.Write(string.Format(" {0} ", _field[c]).PadLeft(4));
}
Console.Out.Write(" || ");
for (int y = 0; y < _length; y++)
{
int c = Get1DCoord(x, y);
if (c == cell)
Console.Out.Write(string.Format("[{0}]", _metric[c]).PadLeft(4));
else
Console.Out.Write(string.Format(" {0} ", _metric[c]).PadLeft(4));
}
Console.Out.WriteLine();
}
Console.Out.WriteLine();
}
}
}
产生的轰炸模式输出如下(左边是字段值，右边是度量值)
Round 1:
2 1 4 2 3 2 6 || 7 16 8 10 4 18 6
3 5 3 1 1 1 9 || 11 18 18 21 17 28 5
4 [2] 4 2 3 4 1 || 19 [32] 21 20 17 24 22
7 6 2 4 4 3 6 || 8 17 20 14 16 22 8
1 2 1 1 1 2 4 || 14 15 14 11 13 16 7
Round 2:
2 1 4 2 3 2 6 || 5 13 6 9 4 18 6
2 4 2 1 1 [1] 9 || 10 15 17 19 17 [28] 5
3 2 3 2 3 4 1 || 16 24 18 17 17 24 22
6 5 1 4 4 3 6 || 7 14 19 12 16 22 8
1 2 1 1 1 2 4 || 12 12 12 10 13 16 7
Round 3:
2 1 4 2 2 1 5 || 5 13 6 7 3 15 5
2 4 2 1 0 1 8 || 10 15 17 16 14 20 2
3 [2] 3 2 2 3 0 || 16 [24] 18 15 16 21 21
6 5 1 4 4 3 6 || 7 14 19 11 14 19 6
1 2 1 1 1 2 4 || 12 12 12 10 13 16 7
Round 4:
2 1 4 2 2 1 5 || 3 10 4 6 3 15 5
1 3 1 1 0 1 8 || 9 12 16 14 14 20 2
2 2 2 2 2 [3] 0 || 13 16 15 12 16 [21] 21
5 4 0 4 4 3 6 || 6 11 18 9 14 19 6
1 2 1 1 1 2 4 || 10 9 10 9 13 16 7
Round 5:
2 1 4 2 2 1 5 || 3 10 4 6 2 13 3
1 3 1 1 0 [0] 7 || 9 12 16 13 12 [19] 2
2 2 2 2 1 3 0 || 13 16 15 10 14 15 17
5 4 0 4 3 2 5 || 6 11 18 7 13 17 6
1 2 1 1 1 2 4 || 10 9 10 8 11 13 5
Round 6:
2 1 4 2 1 0 4 || 3 10 4 5 2 11 2
1 3 1 1 0 0 6 || 9 12 16 11 8 13 0
2 2 2 2 0 2 0 || 13 16 15 9 14 14 15
5 4 [0] 4 3 2 5 || 6 11 [18] 6 11 15 5
1 2 1 1 1 2 4 || 10 9 10 8 11 13 5
Round 7:
2 1 4 2 1 0 4 || 3 10 4 5 2 11 2
1 3 1 1 0 0 6 || 8 10 13 9 7 13 0
2 [1] 1 1 0 2 0 || 11 [15] 12 8 12 14 15
5 3 0 3 3 2 5 || 3 8 10 3 8 15 5
1 1 0 0 1 2 4 || 8 8 7 7 9 13 5
Round 8:
2 1 4 2 1 0 4 || 1 7 2 4 2 11 2
0 2 0 1 0 0 6 || 7 7 12 7 7 13 0
1 1 0 1 0 2 0 || 8 8 10 6 12 14 15
4 2 0 3 3 [2] 5 || 2 6 8 2 8 [15] 5
1 1 0 0 1 2 4 || 6 6 6 7 9 13 5
Round 9:
2 1 4 2 1 0 4 || 1 7 2 4 2 11 2
0 2 0 1 0 0 6 || 7 7 12 7 6 12 0
1 1 0 1 0 [1] 0 || 8 8 10 5 10 [13] 13
4 2 0 3 2 2 4 || 2 6 8 0 6 9 3
1 1 0 0 0 1 3 || 6 6 6 5 8 10 4
Round 10:
2 1 4 2 1 0 4 || 1 7 2 4 2 10 1
0 2 [0] 1 0 0 5 || 7 7 [12] 7 6 11 0
1 1 0 1 0 1 0 || 8 8 10 4 8 9 10
4 2 0 3 1 1 3 || 2 6 8 0 6 8 3
1 1 0 0 0 1 3 || 6 6 6 4 6 7 2
Round 11:
2 0 3 1 1 0 4 || 0 6 0 3 0 10 1
0 1 0 0 0 [0] 5 || 4 5 5 5 3 [11] 0
1 0 0 0 0 1 0 || 6 8 6 4 6 9 10
4 2 0 3 1 1 3 || 1 5 6 0 5 8 3
1 1 0 0 0 1 3 || 6 6 6 4 6 7 2
Round 12:
2 0 3 1 0 0 3 || 0 6 0 2 1 7 1
0 1 0 0 0 0 4 || 4 5 5 4 1 7 0
1 0 0 0 0 [0] 0 || 6 8 6 4 5 [9] 8
4 2 0 3 1 1 3 || 1 5 6 0 4 7 2
1 1 0 0 0 1 3 || 6 6 6 4 6 7 2
Round 13:
2 0 3 1 0 0 3 || 0 6 0 2 1 6 0
0 1 0 0 0 0 3 || 4 5 5 4 1 6 0
1 [0] 0 0 0 0 0 || 6 [8] 6 3 3 5 5
4 2 0 3 0 0 2 || 1 5 6 0 4 6 2
1 1 0 0 0 1 3 || 6 6 6 3 4 4 0
Round 14:
2 0 3 1 0 [0] 3 || 0 5 0 2 1 [6] 0
0 0 0 0 0 0 3 || 2 5 4 4 1 6 0
0 0 0 0 0 0 0 || 4 4 4 3 3 5 5
3 1 0 3 0 0 2 || 0 4 5 0 4 6 2
1 1 0 0 0 1 3 || 4 4 5 3 4 4 0
Round 15:
2 0 3 1 0 0 2 || 0 5 0 2 1 4 0
0 0 0 0 0 0 2 || 2 5 4 4 1 4 0
0 0 0 0 0 0 0 || 4 4 4 3 3 4 4
3 1 0 3 0 [0] 2 || 0 4 5 0 4 [6] 2
1 1 0 0 0 1 3 || 4 4 5 3 4 4 0
Round 16:
2 [0] 3 1 0 0 2 || 0 [5] 0 2 1 4 0
0 0 0 0 0 0 2 || 2 5 4 4 1 4 0
0 0 0 0 0 0 0 || 4 4 4 3 3 3 3
3 1 0 3 0 0 1 || 0 4 5 0 3 3 1
1 1 0 0 0 0 2 || 4 4 5 3 3 3 0
Round 17:
1 0 2 1 0 0 2 || 0 3 0 1 1 4 0
0 0 0 0 0 0 2 || 1 3 3 3 1 4 0
0 0 0 0 0 0 0 || 4 4 4 3 3 3 3
3 1 [0] 3 0 0 1 || 0 4 [5] 0 3 3 1
1 1 0 0 0 0 2 || 4 4 5 3 3 3 0
Round 18:
1 0 2 1 0 0 2 || 0 3 0 1 1 4 0
0 0 0 0 0 0 2 || 1 3 3 3 1 4 0
0 0 0 0 0 0 0 || 3 3 2 2 2 3 3
3 [0] 0 2 0 0 1 || 0 [4] 2 0 2 3 1
1 0 0 0 0 0 2 || 2 4 2 2 2 3 0
Round 19:
1 0 2 1 0 [0] 2 || 0 3 0 1 1 [4] 0
0 0 0 0 0 0 2 || 1 3 3 3 1 4 0
0 0 0 0 0 0 0 || 2 2 2 2 2 3 3
2 0 0 2 0 0 1 || 0 2 2 0 2 3 1
0 0 0 0 0 0 2 || 2 2 2 2 2 3 0
Round 20:
1 [0] 2 1 0 0 1 || 0 [3] 0 1 1 2 0
0 0 0 0 0 0 1 || 1 3 3 3 1 2 0
0 0 0 0 0 0 0 || 2 2 2 2 2 2 2
2 0 0 2 0 0 1 || 0 2 2 0 2 3 1
0 0 0 0 0 0 2 || 2 2 2 2 2 3 0
Round 21:
0 0 1 1 0 0 1 || 0 1 0 0 1 2 0
0 0 0 0 0 0 1 || 0 1 2 2 1 2 0
0 0 0 0 0 0 0 || 2 2 2 2 2 2 2
2 0 0 2 0 [0] 1 || 0 2 2 0 2 [3] 1
0 0 0 0 0 0 2 || 2 2 2 2 2 3 0
Round 22:
0 0 1 1 0 0 1 || 0 1 0 0 1 2 0
0 0 0 0 0 0 1 || 0 1 2 2 1 2 0
[0] 0 0 0 0 0 0 || [2] 2 2 2 2 1 1
2 0 0 2 0 0 0 || 0 2 2 0 2 1 1
0 0 0 0 0 0 1 || 2 2 2 2 2 1 0
Round 23:
0 0 1 1 0 0 1 || 0 1 0 0 1 2 0
0 0 [0] 0 0 0 1 || 0 1 [2] 2 1 2 0
0 0 0 0 0 0 0 || 1 1 2 2 2 1 1
1 0 0 2 0 0 0 || 0 1 2 0 2 1 1
0 0 0 0 0 0 1 || 1 1 2 2 2 1 0
Round 24:
0 0 0 0 0 0 1 || 0 0 0 0 0 2 0
0 0 0 0 0 0 1 || 0 0 0 0 0 2 0
0 0 [0] 0 0 0 0 || 1 1 [2] 2 2 1 1
1 0 0 2 0 0 0 || 0 1 2 0 2 1 1
0 0 0 0 0 0 1 || 1 1 2 2 2 1 0
Round 25:
0 0 0 0 0 [0] 1 || 0 0 0 0 0 [2] 0
0 0 0 0 0 0 1 || 0 0 0 0 0 2 0
0 0 0 0 0 0 0 || 1 1 1 1 1 1 1
1 0 0 1 0 0 0 || 0 1 1 0 1 1 1
0 0 0 0 0 0 1 || 1 1 1 1 1 1 0
Round 26:
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
[0] 0 0 0 0 0 0 || [1] 1 1 1 1 0 0
1 0 0 1 0 0 0 || 0 1 1 0 1 1 1
0 0 0 0 0 0 1 || 1 1 1 1 1 1 0
Round 27:
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 [0] 0 0 0 0 || 0 0 [1] 1 1 0 0
0 0 0 1 0 0 0 || 0 0 1 0 1 1 1
0 0 0 0 0 0 1 || 0 0 1 1 1 1 0
Round 28:
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 0 0 0 0 0 || 0 0 0 0 0 0 0
0 0 0 0 0 [0] 0 || 0 0 0 0 0 [1] 1
0 0 0 0 0 0 1 || 0 0 0 0 0 1 0
Done in 28 rounds
这是部分答案，我试图找到一个下界和上界，可能是炸弹的数量。
在3x3和更小的板上，解决方案通常是编号最大的单元。
在大于4x4的板中，第一个明显的下界是角的和:
*2* 3 7 *1*
1 5 6 2
2 1 3 2
*6* 9 6 *4*
无论你如何安排炸弹，都不可能用少于2+1+6+4=13个炸弹来清除这个4x4板。
在其他回答中已经提到，将炸弹放置在第二个角落以消除角落并不比将炸弹放置在角落本身更糟糕，所以考虑到棋盘:
*2* 3 4 7 *1*
1 5 2 6 2
4 3 4 2 1
2 1 2 4 1
3 1 3 4 1
2 1 4 3 2
*6* 9 1 6 *4*
我们可以通过在第二个角上放置炸弹来将角归零，从而得到一个新的板:
0 1 1 6 0
0 3 0 5 1
2 1 1 1 0
2 1 2 4 1
0 0 0 0 0
0 0 0 0 0
0 3 0 2 0
到目前为止一切顺利。我们需要13枚炸弹才能清空角落。
现在观察下面标记的数字6、4、3和2:
0 1 1 *6* 0
0 3 0 5 1
2 1 1 1 0
*2* 1 2 *4* 1
0 0 0 0 0
0 0 0 0 0
0 *3* 0 2 0
我们无法使用一枚炸弹去轰炸任何两个细胞，所以最小炸弹数量增加了6+4+3+2，所以再加上我们用来清除角落的炸弹数量，我们得到这张地图所需的最小炸弹数量变成了28枚炸弹。用少于28个炸弹是不可能清除这张地图的，这是这张地图的下限。
可以用贪心算法建立上界。其他答案表明，贪婪算法产生的解决方案使用28个炸弹。因为我们之前已经证明了没有一个最优解可以拥有少于28个炸弹，所以28个炸弹确实是一个最优解。
当贪心和我上面提到的寻找最小界的方法不收敛时，我猜你必须回去检查所有的组合。
求下界的算法如下:
选一个数值最大的元素，命名为P。 将所有距离P和P本身两步远的单元格标记为不可拾取。 将P添加到最小值列表中。 重复步骤1，直到所有单元格都不可拾取。 对最小值列表求和得到下界。
这是另一个想法:
让我们先给黑板上的每个空格分配一个权重，计算在那里扔炸弹会减少多少数字。如果这个空间有一个非零数，它就得到一个点，如果它的相邻空间有一个非零数，它就得到一个额外的点。如果这是一个1000 * 1000的网格，我们为这100万个空间中的每一个都分配了权重。
然后根据权重对列表中的空格进行排序，并轰炸权重最高的空格。可以这么说，这是我们最大的收获。
在此之后，更新每个空间的重量是受炸弹的影响。这是你轰炸的空间，和它相邻的空间，以及它们相邻的空间。换句话说，任何空间的价值都可能因为爆炸而减少为零，或者相邻空间的价值减少为零。
然后，根据权重重新排序列表空间。由于轰炸只改变了一小部分空间的权重，因此不需要使用整个列表，只需在列表中移动这些空间。
轰炸新的最高权重空间，并重复上述步骤。
这保证了每次轰炸都能减少尽可能多的空格(基本上，它会击中尽可能少的已经为零的空格)，所以这是最优的，除非它们的权重是相同的。所以你可能需要做一些回溯跟踪，当有一个平局的顶部重量。不过，只有最高重量的领带重要，其他领带不重要，所以希望没有太多的回溯。
Edit: Mysticial's counterexample below demonstrates that in fact this isn't guaranteed to be optimal, regardless of ties in weights. In some cases reducing the weight as much as possible in a given step actually leaves the remaining bombs too spread out to achieve as high a cummulative reduction after the second step as you could have with a slightly less greedy choice in the first step. I was somewhat mislead by the notion that the results are insensitive to the order of bombings. They are insensitive to the order in that you could take any series of bombings and replay them from the start in a different order and end up with the same resulting board. But it doesn't follow from that that you can consider each bombing independently. Or, at least, each bombing must be considered in a way that takes into account how well it sets up the board for subsequent bombings.
这里似乎有一个非二部匹配子结构。考虑下面的例子:
0010000
1000100
0000001
1000000
0000001
1000100
0010000
这种情况下的最佳解决方案的大小为5，因为这是9-cycle的边的最小顶点覆盖的大小。
这个例子，特别地，表明了一些人发布的线性规划松弛法是不精确的，不管用，还有其他一些不好的东西。我很确定我可以减少“用尽可能少的边覆盖我的平面立方图的顶点”来解决你的问题，这让我怀疑任何贪婪/爬坡的解决方案是否有效。
在最坏的情况下，我找不到在多项式时间内解出来的方法。可能有一个非常聪明的二进制搜索和dp解决方案，但我没有看到。
编辑:我看到这个比赛(http://deadline24.pl)是语言无关的;他们给你一堆输入文件，你给他们输出。所以你不需要在最坏情况下多项式时间内运行的东西。特别是，您可以查看输入!
There are a bunch of small cases in the input. Then there's a 10x1000 case, a 100x100 case, and a 1000x1000 case. The three large cases are all very well-behaved. Horizontally adjacent entries typically have the same value. On a relatively beefy machine, I'm able to solve all of the cases by brute-forcing using CPLEX in just a couple of minutes. I got lucky on the 1000x1000; the LP relaxation happens to have an integral optimal solution. My solutions agree with the .ans files provided in the test data bundle.
我敢打赌你可以用比我更直接的方式使用输入的结构，如果你看了它;看起来你只需要砍掉第一行，或者两行，或者三行直到你什么都不剩。(看起来，在1000x1000中，所有的行都是不增加的?我猜这就是你的“B部分”的来源吧?)
所有这些问题都归结为计算编辑距离。简单地计算给定矩阵和零矩阵之间的Levenshtein距离的变体，其中编辑被轰炸替换，使用动态编程来存储中间数组之间的距离。我建议使用矩阵的哈希作为键。在pseudo-Python:
memo = {}
def bomb(matrix,i,j):
# bomb matrix at i,j
def bombsRequired(matrix,i,j):
# bombs required to zero matrix[i,j]
def distance(m1, i, len1, m2, j, len2):
key = hash(m1)
if memo[key] != None:
return memo[key]
if len1 == 0: return len2
if len2 == 0: return len1
cost = 0
if m1 != m2: cost = m1[i,j]
m = bomb(m1,i,j)
dist = distance(str1,i+1,len1-1,str2,j+1,len2-1)+cost)
memo[key] = dist
return dist
