有一种恐怖，叫大爆搜
Posted Loser Of Life
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到目前这个阶段，大爆搜做了好几个，有必要做一下小的总结了。
玛雅游戏：出门左转 http://www.cnblogs.com/Loser-of-Life/p/7247413.html的A
斗地主：出门右转http://www.cnblogs.com/Loser-of-Life/p/7259858.html的B
天鹅会面：出门直行http://www.cnblogs.com/Loser-of-Life/p/7295770.html的A
引水入城：链接：http://cogs.pro/cogs/problem/problem.php?pid=521
先正向$bfs$判断一下是否存在解，然后反向$bfs$，运用贪心策略选择最长线段进行覆盖。
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<queue> 6 using namespace std; 7 const int maxn=505; 8 int a[maxn][maxn],mp[maxn][maxn],l[maxn][maxn],r[maxn][maxn],n,m; 9 int px[4]={1,-1,0,0},py[4]={0,0,1,-1}; 10 typedef pair<int,int> pii; 11 void bfs(int b[maxn][maxn],int x,int y,int v,int f) 12 { 13 queue<pii>q;q.push(make_pair(x,y));b[x][y]=v; 14 while(!q.empty()) 15 { 16 pii p=q.front();q.pop(); 17 x=p.first,y=p.second; 18 for(int i=0;i<4;i++) 19 { 20 int nowx=x+px[i],nowy=y+py[i]; 21 if(nowx<1||nowx>n||nowy<1||nowy>m||b[nowx][nowy])continue; 22 if(!f&&a[nowx][nowy]>=a[x][y])continue; 23 if(f&&a[nowx][nowy]<=a[x][y])continue; 24 b[nowx][nowy]=b[x][y]; 25 q.push(make_pair(nowx,nowy)); 26 } 27 } 28 } 29 struct data 30 { 31 int l,r; 32 }c[maxn]; 33 inline bool cmp(data a,data b) 34 { 35 if(a.l!=b.l)return a.l<b.l; 36 return a.r<b.r; 37 } 38 int haha() 39 { 40 freopen("flow.in","r",stdin); 41 freopen("flow.out","w",stdout); 42 scanf("%d%d",&n,&m); 43 for(int i=1;i<=n;i++) 44 for(int j=1;j<=m;j++)scanf("%d",&a[i][j]); 45 for(int i=1;i<=m;i++)bfs(mp,1,i,1,0); 46 int tot=0; 47 for(int i=1;i<=m;i++) 48 if(!mp[n][i])tot++; 49 if(tot) 50 { 51 printf("0\\n%d\\n",tot); 52 return 0; 53 } 54 for(int i=1;i<=m;i++) 55 if(!l[n][i])bfs(l,n,i,i,1); 56 for(int i=m;i;i--) 57 if(!r[n][i])bfs(r,n,i,i,1); 58 for(int i=1;i<=m;i++) 59 { 60 if(!l[1][i])l[1][i]=r[1][i]; 61 if(!r[1][i])r[1][i]=l[1][i]; 62 c[i].l=l[1][i],c[i].r=r[1][i]; 63 } 64 sort(c+1,c+m+1,cmp); 65 int now=0,to=0; 66 for(int i=1;i<=m;i++) 67 if(now+1>=c[i].l)to=max(to,c[i].r); 68 else 69 { 70 now=to; 71 to=max(to,c[i].r); 72 tot++; 73 } 74 if(now!=m)tot++; 75 printf("1\\n%d\\n",tot); 76 } 77 int sb=haha(); 78 int main(){;}
靶形数独：链接：http://cogs.pro/cogs/problem/problem.php?pid=407
说好的状压启发式搜索呢？怎么是裸的$dfs$？虽然我很喜欢……港真，我今天下午颓了半下午这道题样例……和$wcx$比赛数独结果对面最后还剩两步发现他全错……欢声笑语中打出$GG$……
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 using namespace std; 6 struct node 7 { 8 int x,y; 9 }V[101]; 10 int v[9][9]={ 11 {1,1,1,2,2,2,3,3,3}, 12 {1,1,1,2,2,2,3,3,3}, 13 {1,1,1,2,2,2,3,3,3}, 14 {4,4,4,5,5,5,6,6,6}, 15 {4,4,4,5,5,5,6,6,6}, 16 {4,4,4,5,5,5,6,6,6}, 17 {7,7,7,8,8,8,9,9,9}, 18 {7,7,7,8,8,8,9,9,9}, 19 {7,7,7,8,8,8,9,9,9} 20 },x,ans=-1,tim=0; 21 int w[9][9]={ 22 {6,6,6,6,6,6,6,6,6}, 23 {6,7,7,7,7,7,7,7,6}, 24 {6,7,8,8,8,8,8,7,6}, 25 {6,7,8,9,9,9,8,7,6}, 26 {6,7,8,9,10,9,8,7,6}, 27 {6,7,8,9,9,9,8,7,6}, 28 {6,7,8,8,8,8,8,7,6}, 29 {6,7,7,7,7,7,7,7,6}, 30 {6,6,6,6,6,6,6,6,6} 31 },tot=0; 32 int vis[10][10],lx[10][10],ly[10][10]; 33 void dfs(int rem,int now) 34 { 35 if(!rem) 36 { 37 ans=max(ans,now); 38 return; 39 } 40 for(int i=1;i<=9;i++) 41 if(!vis[v[V[rem].x][V[rem].y]][i]&&!lx[V[rem].x][i]&&!ly[V[rem].y][i]) 42 { 43 vis[v[V[rem].x][V[rem].y]][i]=1; 44 lx[V[rem].x][i]=1; 45 ly[V[rem].y][i]=1; 46 dfs(rem-1,now+w[V[rem].x][V[rem].y]*i); 47 vis[v[V[rem].x][V[rem].y]][i]=0; 48 lx[V[rem].x][i]=0; 49 ly[V[rem].y][i]=0; 50 } 51 } 52 int haha() 53 { 54 freopen("sudoku.in","r",stdin); 55 freopen("sudoku.out","w",stdout); 56 int stat=0; 57 for(int i=0;i<9;i++) 58 for(int j=0;j<9;j++) 59 { 60 int x;scanf("%d",&x); 61 if(!x)V[++tot]=(node){i,j}; 62 else 63 { 64 stat+=x*w[i][j]; 65 vis[v[i][j]][x]=lx[i][x]=ly[j][x]=1; 66 } 67 } 68 dfs(tot,stat); 69 printf("%d\\n",ans); 70 } 71 int sb=haha(); 72 int main(){;}
传染病控制：链接：http://cogs.pro/cogs/problem/problem.php?pid=107
果然$CCF$老爷机啊……正常情况下每一次都是要剪枝的，但是在评测机上直接裸$dfs$，每一层暴力判断，改都不改就过了……
1 #include<iostream> 2 #include<cstring> 3 #include<cstdio> 4 #include<algorithm> 5 using namespace std; 6 const int maxn=310; 7 struct node 8 { 9 int from,to,next; 10 }edge[maxn<<1]; 11 int head[maxn],tot; 12 void addedge(int u,int v) 13 { 14 edge[++tot]=(node){u,v,head[u]};head[u]=tot; 15 } 16 int fa[maxn],n,m,deep[maxn][maxn]; 17 bool cutt[maxn]; 18 void cut(int root) 19 { 20 cutt[root]=1; 21 for(int i=head[root];i;i=edge[i].next) 22 { 23 int v=edge[i].to; 24 if(v!=fa[root])cut(v); 25 } 26 } 27 void rebuild(int root) 28 { 29 cutt[root]=0; 30 for(int i=head[root];i;i=edge[i].next) 31 { 32 int v=edge[i].to; 33 if(v!=fa[root])rebuild(v); 34 } 35 } 36 int siz[maxn]; 37 void dfs(int root,int dep) 38 { 39 siz[root]=1;deep[dep][++deep[dep][0]]=root; 40 for(int i=head[root];i;i=edge[i].next) 41 { 42 int v=edge[i].to; 43 if(v!=fa[root]) 44 { 45 fa[v]=root; 46 dfs(v,dep+1); 47 siz[root]+=siz[v]; 48 } 49 } 50 } 51 int maxl=-1; 52 void dfss(int dep,int num) 53 { 54 maxl=max(maxl,num); 55 for(int i=1;i<=deep[dep][0];i++) 56 if(!cutt[deep[dep][i]]) 57 { 58 cut(deep[dep][i]); 59 dfss(dep+1,num+siz[deep[dep][i]]); 60 rebuild(deep[dep][i]); 61 } 62 } 63 int haha() 64 { 65 freopen("epidemic.in","r",stdin); 66 freopen("epidemic.out","w",stdout); 67 scanf("%d%d",&n,&m); 68 for(int i=1;i<=m;i++) 69 { 70 int u,v;scanf("%d%d",&u,&v); 71 addedge(u,v);addedge(v,u); 72 } 73 dfs(1,1); 74 dfss(2,0); 75 printf("%d\\n",n-maxl); 76 //for(int i=1;i<=n;i++)cout<<siz[i]<<" "; 77 //puts(""); 78 } 79 int sb=haha(); 80 int main(){;}
字串变换：链接：http://cogs.pro/cogs/problem/problem.php?pid=65
这果然是那个没有$STL$的时代啊……原来可是要$Hash$加$Treap$判重的，现在$std::queue$、$std::queue$、$std::map$、$std::string$直接碾压……除去这些，就是一个双向广搜。
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<map> 6 #include<string> 7 #include<queue> 8 using namespace std; 9 struct node 10 { 11 string s;int num; 12 }; 13 queue<node>q1,q2; 14 map<string,int>m1,m2; 15 string changings[6][2]; 16 int cnt,ans; 17 string become(string now,int pos,int n,string tmp) 18 { 19 return now.replace(pos,n,tmp); 20 } 21 bool dbfs() 22 { 23 while(!q1.empty()&&!q2.empty()) 24 { 25 node s1=q1.front(),s2;q1.pop(); 26 int len=s1.s.size(); 27 for(int i=0;i<len;i++) 28 for(int j=0;j<cnt;j++) 29 { 30 int siz=changings[j][0].size(); 31 if(i+siz-1<len&&!s1.s.compare(i,siz,changings[j][0])&&!m1.count(become(s1.s,i,siz,changings[j][1]))) 32 { 33 s2.s=become(s1.s,i,siz,changings[j][1]); 34 s2.num=s1.num+1; 35 if(s2.num>10)return 0; 36 m1[s2.s]=s2.num;q1.push(s2); 37 if(m2.count(s2.s)) 38 { 39 ans=s2.num+m2[s2.s]; 40 return 1; 41 } 42 } 43 } 44 s1=q2.front(),s2;q2.pop(); 45 len=s1.s.size(); 46 for(int i=0;i<len;i++) 47 for(int j=0;j<cnt;j++) 48 { 49 int siz=changings[j][1].size(); 50 if(i+siz-1<len&&!s1.s.compare(i,siz,changings[j][1])&&!m2.count(become(s1.s,i,siz,changings[j][0]))) 51 { 52 s2.s=become(s1.s,i,siz,changings[j][0]); 53 s2.num=s1.num+1; 54 if(s2.num>10)return 0; 55 m2[s2.s]=s2.num;q2.push(s2); 56 if(m1.count(s2.s)) 57 { 58 ans=s2.num+m1[s2.s]; 59 return 1; 60 } 61 } 62 } 63 } 64 return 0; 65 } 66 int haha() 67 { 68 freopen("string.in","r",stdin); 69 freopen("string.out","w",stdout); 70 node a,b;cin>>a.s>>b.s; 71 if(a.s==b.s) 72 { 73 cout<<0; 74 return 020190918CF训练