2012 Asia Hangzhou Regional Contest--hdu4462Scaring the Birds(IDA)

题目请戳这里

题目大意：

有一个n*n的格子，有k个空地，其他地方都种的有庄稼。现在要在k个空地中放稻草人保护庄稼，每个稻草人罩附近距离他曼哈顿距离不超过r的点，求最少需要多少个稻草人能罩住所有的庄稼。

题目分析：k太小了，n太小了，IDA爆搜之。

不过跑的好慢啊，hdu rank倒数第一。。。

详情请见代码：

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<cctype>
#include<map>
#include<vector>
#include<set>
#include<queue>
#include<string>
#include<ctime>
using namespace std;
const int N = 51;
const int M = 10000005;
const int inf = 0x3f3f3f3f;
const double eps = 1e-6;
const double PI = acos(-1.0);
typedef __int64 ll;

int flag

;
bool used
;
struct node
{
int x,y,r;
}pt
;
int n,k;
int ans,corns;
bool ok;

int put(int id)
{
int i,j;
int row,col;
int ret = 0;
row = pt[id].x - pt[id].r;
if(row < 1)
row = 1;
for(i = row,col = pt[id].r - (pt[id].x - row);i <= pt[id].x;i ++,col ++)
{
int l,r;
l = max(1,pt[id].y - col);
r = min(n,pt[id].y + col);
for(j = l;j <= r;j ++)
{
flag[i][j] ++;
if(flag[i][j] == 1)
ret ++;
}
}
row = pt[id].x + pt[id].r;
if(row > n)
row = n;
for(i = pt[id].x + 1,col = pt[id].r - 1;i <= row;i ++,col --)
{
int l,r;
l = max(1,pt[id].y - col);
r = min(n,pt[id].y + col);
for(j = l;j <= r;j ++)
{
flag[i][j] ++;
if(flag[i][j] == 1)
ret ++;
}
}
return ret;
}
void disput(int id)
{
int i,j;
int row,col;
row = pt[id].x - pt[id].r;
if(row < 1)
row = 1;
for(i = row,col = pt[id].r - (pt[id].x - row);i <= pt[id].x;i ++,col ++)
{
int l,r;
l = max(1,pt[id].y - col);
r = min(n,pt[id].y + col);
for(j = l;j <= r;j ++)
{
flag[i][j] --;
}
}
row = pt[id].x + pt[id].r;
if(row > n)
row = n;
for(i = pt[id].x + 1,col = pt[id].r - 1;i <= row;i ++,col --)
{
int l,r;
l = max(1,pt[id].y - col);
r = min(n,pt[id].y + col);
for(j = l;j <= r;j ++)
{
flag[i][j] --;
}
}
}
void show()
{
for(int i = 1;i <= n;i ++)
{
for(int j = 1;j <= n;j ++)
printf("%4d",flag[i][j]);
putchar(10);
}
}
void dfs(int dp,int last)
{
if(last == 0)
{
ok = true;
return;
}
//show();
if(dp >= ans)
return;
if(ok)
return;

int i;
for(i = 1;i <= k;i ++)
{
if(used[i])
continue;
used[i] = true;
int tmp = put(i);
dfs(dp + 1,last - tmp);
disput(i);
used[i] = false;
}
}
int main()
{
int i;
while(scanf("%d",&n),n)
{
scanf("%d",&k);
memset(flag,0,sizeof(flag));
for(i = 1;i <= k;i ++)
{
scanf("%d%d",&pt[i].x,&pt[i].y);
flag[pt[i].x][pt[i].y] = inf;
}
for(i = 1;i <= k;i ++)
scanf("%d",&pt[i].r);
corns = n * n - k;
if(corns <= 0)
{
printf("0\n");
continue;
}
ans = 0;
ok = false;
memset(used,false,sizeof(used));
while(1)
{
ans ++;
dfs(0,corns);
if(ok || ans >= k)
break;
}
if(ok)
printf("%d\n",ans);
else
printf("-1\n");
}
return 0;
}