我必須遍歷一個矩陣,並說出它有多少個「特徵區域」。回溯到haskell
特徵區域被定義爲值爲n或> n的元素相鄰的區域。
例如,給定的矩陣:
0 1 2 2
0 1 1 2
0 3 0 0
有1型的單個特徵區域,其等於原始矩陣:
0 1 2 2
0 1 1 2
0 3 0 0
有2類型的兩個特徵方面:
0 0 2 2 0 0 0 0
0 0 0 2 0 0 0 0
0 0 0 0 0 3 0 0
而且還有一個類型3的特徵區域:
0 0 0 0
0 0 0 0
0 3 0 0
所以,在函數調用:
countAreas [[0,1,2,2],[0,1,1,2],[0,3,0,0]]
結果應該是
[1,2,1]
我還沒有定義countAreas然而,我堅持我的visit
功能時,它有沒有更多可能的廣場在其中移動它卡住,並沒有進行適當的遞歸調用。我是函數式編程的新手,我仍在摸索如何在這裏實現回溯算法。看看我的代碼,我可以做些什麼來改變它?
move_right :: (Int,Int) -> [[Int]] -> Int -> Bool
move_right (i,j) mat cond | (j + 1) < number_of_columns mat && consult (i,j+1) mat /= cond = True
| otherwise = False
move_left :: (Int,Int) -> [[Int]] -> Int -> Bool
move_left (i,j) mat cond | (j - 1) >= 0 && consult (i,j-1) mat /= cond = True
| otherwise = False
move_up :: (Int,Int) -> [[Int]] -> Int -> Bool
move_up (i,j) mat cond | (i - 1) >= 0 && consult (i-1,j) mat /= cond = True
| otherwise = False
move_down :: (Int,Int) -> [[Int]] -> Int -> Bool
move_down (i,j) mat cond | (i + 1) < number_of_rows mat && consult (i+1,j) mat /= cond = True
| otherwise = False
imp :: (Int,Int) -> Int
imp (i,j) = i
number_of_rows :: [[Int]] -> Int
number_of_rows i = length i
number_of_columns :: [[Int]] -> Int
number_of_columns (x:xs) = length x
consult :: (Int,Int) -> [[Int]] -> Int
consult (i,j) l = (l !! i) !! j
visited :: (Int,Int) -> [(Int,Int)] -> Bool
visited x y = elem x y
add :: (Int,Int) -> [(Int,Int)] -> [(Int,Int)]
add x y = x:y
visit :: (Int,Int) -> [(Int,Int)] -> [[Int]] -> Int -> [(Int,Int)]
visit (i,j) vis mat cond | move_right (i,j) mat cond && not (visited (i,j+1) vis) = visit (i,j+1) (add (i,j+1) vis) mat cond
| move_down (i,j) mat cond && not (visited (i+1,j) vis) = visit (i+1,j) (add (i+1,j) vis) mat cond
| move_left (i,j) mat cond && not (visited (i,j-1) vis) = visit (i,j-1) (add (i,j-1) vis) mat cond
| move_up (i,j) mat cond && not (visited (i-1,j) vis) = visit (i-1,j) (add (i-1,j) vis) mat cond
| otherwise = vis
'0 1 0 0; 0 1 1 0; 0 0 0 0''? – kennytm 2010-04-12 16:08:40
我不明白,不應該第一個矩陣[[0 1 2 2] [0 1 1 2] [0 3 0 0]]的類型1區域是 [[0 1 2 2] [0 1 1 2] [0 ** 0 ** 0 0]]? – 2010-04-12 16:17:19
是的,我最初發布時犯了一個錯誤。相鄰區域的值應爲n或> n。 – andandandand 2010-04-12 17:43:50