状态压缩动态规划 -- 棋盘问题 POJ 1321

一个 N * N 的棋盘上面，有些格子不能放，放置 M 的棋子，

每两个棋子不能在同一行或者同一列，问有多少种放法

DFS太慢，用SCR好点点

Python 只有 22 行，其实可以更短，但是得排成很长很长的一行

while True:
    table = [ [ 0 for j in range( 300 ) ] for i in range( 12 ) ]
    table[0][0] = 1
    boardsize, chessnum = map( int, raw_input().split() )
    if boardsize == chessnum == -1: break
    states = range( 1 << boardsize )
    cols = raws = range( 1, boardsize + 1 )
    chessboard = dict( zip( raws, [ ' ' + raw_input() for i in raws ] ) )
    ones = dict( zip( states, map( lambda s: str( bin( s ) ).count( '1' ), states ) ) )

    for raw in raws:
        for state in states:
            if ones[state] <= chessnum:
                table[raw][state] += table[raw - 1][state]
                for col in cols:
                    s = 1 << ( col - 1 )
                    if chessboard[raw][col] == '#' and state & s == 0:
                        nextstate = state | s
                        table[raw][nextstate] += table[raw - 1][state]

    print sum( [ table[boardsize][state] for state in states if ones[state] == chessnum ] )

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