UVa 387 A Puzzling Problem

题目链接:http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=109&page=show_problem&problem=323

题目描述：给定几个图形，问能否拼成一个4*4的矩形

分析：这个题虽然放在难回溯里，但因为没有旋转翻转之类的操作，所以不是很难。一行一行的放就行了。

#include <cstdio>
#include <cstring>

const int MAXN = 10;

struct piece
{
    int r, c;
    char tu[MAXN][MAXN];
};

piece P[210];
char map[MAXN][MAXN];
bool vis[210];
int n;

void putdown( int cur, int x, int y )
{
    for ( int i = 0; i < P[cur].r; ++i )
        for ( int j = 0; j < P[cur].c; ++j )
        {
            if ( P[cur].tu[i][j] - '0' )
                map[x + i][y + j] = cur + 1 + '0';
        }
    return;
}

void clear( int cur, int x, int y )
{
    for ( int i = 0; i < P[cur].r; ++i )
        for ( int j = 0; j < P[cur].c; ++j )
        {
            if ( P[cur].tu[i][j] - '0' )
                map[x + i][y + j] = '*';
        }
    return;
}

bool check( int cur, int x, int y )
{
    for ( int i = 0; i < P[cur].r; ++i )
        for ( int j = 0; j < P[cur].c; ++j )
        {
            if ( P[cur].tu[i][j] - '0' )
            {
                if ( map[x + i][y + j] != '*' )
                    return false;

                if ( x + i >= 4 || y + j >= 4 )
                    return false;
            }
        }
    return true;
}

void Print()
{
    for ( int i = 0; i < 4; ++i )
    {
        for ( int j = 0; j < 4; ++j )
            putchar( map[i][j] );
        putchar('\n');
    }
    return;
}

bool DFS( int cur )
{
    if ( cur == n )
    {
        for ( int i = 0; i < 4; ++i )
            for ( int j = 0; j < 4; ++j )
                if ( map[i][j] == '*' ) return false;
        return true;
    }

    for ( int x = 0; x < 4; ++x )
        for ( int y = 0; y < 4; ++y )
        {
            for ( int i = 0; i < n; ++i )
                if ( !vis[i] )
                {
//                    printf("%d %d %d\n", i, x, y);
//                    Print();
                    vis[i] = true;
                    if ( check( cur, x, y ) )
                    {
                        putdown( cur, x, y );
                        if ( DFS( cur + 1 ) ) return true;
                        clear( cur, x, y );
                    }
                    vis[i] = false;
                }
        }

    return false;
}

int main()
{
//    freopen( "s.out", "w", stdout );
    bool notfirst = false;
    while ( scanf( "%d", &n ), n )
    {
        for ( int i = 0; i < n; ++i )
        {
            scanf( "%d%d", &P[i].r, &P[i].c );
            for ( int j = 0; j < P[i].r; ++j )
                scanf( "%s", P[i].tu[j] );
        }

        memset( vis, false, sizeof(vis) );
        memset( map, '*', sizeof(map) );

        if ( notfirst ) puts("");

        if ( DFS( 0 ) ) Print();
        else puts("No solution possible");
        notfirst = true;
    }
    return 0;
}