ZOJ 1002 Fire Net

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深搜题，和八皇后类似，每一个节点，有两个子节点，即放与不放炮台。

#include <stdio.h>#include <string.h>#define MAXN (10+5)int N,amount,MAX;char map[MAXN][MAXN],att[MAXN][MAXN];int max(int x,int y){    return x>y? x:y;}int isvalid( int cloumn,int row ){    int i;    for( i= cloumn -1 ; i>=0 ;i-- )    {        if( att[i][row] == '@' ) return 0;        if( att[i][row] == 'X' ) break;    }    for( i= row -1 ; i>=0 ;i-- )    {        if( att[cloumn][i] == '@' ) return 0;        if( att[cloumn][i] == 'X' ) break;    }    return 1;}void DFS(int cloumn,int row){int next_cloumn,next_row;    if( cloumn == N) {MAX=max(MAX,amount);return ;}if( row+1 == N ) {next_cloumn = cloumn+1;next_row = 0;}else {next_cloumn = cloumn;next_row = row+1;}if( map[cloumn][row] == 'X' ){att[cloumn][row] ='X'; DFS(next_cloumn,next_row);}else{if(  isvalid( cloumn, row ) ){att[cloumn][row] = '@';amount++;DFS(next_cloumn,next_row);amount--;}att[cloumn][row] = '.';DFS( next_cloumn, next_row );}}int main(){    int i;    while( scanf("%d",&N) && N!=0)    {        MAX=0;  amount=0;        memset( att,0,sizeof(att) );        for(i=0;i<N;i++)            scanf( "%s",map[i] );        DFS(0,0);        printf("%d\n",MAX);    }    return 0;}