[bzoj4429] [Nwerc2015] Elementary Math小学数学

Posted 2020-07-26

　　一开始以为是2-sat。。QAQ

　　膜了下题解。。把各个答案离散化后，每对数与答案之间连边，看最大匹配数是否等于n

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 #define ll long long
 6 using namespace std;
 7 const int maxn=2523<<2;
 8 struct zs1{ll v;int id;}a[maxn];
 9 ll b[maxn];int cnt,n1;
10 struct zs{
11     int too,pre;bool flow;
12 }e[233333];int tot,last[maxn];
13 short dis[maxn];
14 int dl[maxn],x[maxn],y[maxn];
15 int i,j,k,n,m,s,t,ans;
16  
17 int ra,fh;char rx;
18 inline int read(){
19     rx=getchar(),ra=0,fh=1;
20     while((rx<‘0‘||rx>‘9‘)&&rx!=‘-‘)rx=getchar();
21     if(rx==‘-‘)fh=-1,rx=getchar();
22     while(rx>=‘0‘&&rx<=‘9‘)ra*=10,ra+=rx-48,rx=getchar();return ra*fh;
23 }
24 inline bool bfs(){
25     memset(dis,0,(t+1)<<1);
26     int l=0,r=1,i,now;dl[1]=s,dis[s]=1;
27     while(l<r&&!dis[t])
28         for(i=last[now=dl[++l]];i;i=e[i].pre)if(e[i].flow&&!dis[e[i].too])
29             dis[e[i].too]=dis[now]+1,dl[++r]=e[i].too;
30 //  for(i=1;i<=t;i++)printf("0->%d  %d\\n",i,dis[i]);
31     return dis[t];
32 }
33 int dfs(int x,int mx){
34     if(x==t)return mx;
35     int used=0,i;bool w;
36     for(i=last[x];i;i=e[i].pre)if(e[i].flow&&dis[e[i].too]==dis[x]+1){
37         w=dfs(e[i].too,1);if(w){
38             e[i].flow=0,e[i^1].flow=1,used+=w;
39             if(used==mx)return used;
40         }
41     }
42     dis[x]=0;return used;
43 }
44 inline void insert(int a,int b){//printf("    %d-->%d\\n",a,b);
45     e[++tot].too=b,e[tot].flow=1,e[tot].pre=last[a],last[a]=tot,
46     e[++tot].too=a,e[tot].flow=0,e[tot].pre=last[b],last[b]=tot;
47 }
48 bool cmp(zs1 a,zs1 b){return a.v<b.v;}
49 int main(){
50     n=read();
51     for(i=1;i<=n;i++)
52         j=x[i]=read(),k=y[i]=read(),
53         a[++n1].v=j+k,a[++n1].v=j-k,a[++n1].v=1LL*j*k,
54         a[n1-2].id=a[n1-1].id=a[n1].id=i;
55     sort(a+1,a+1+n1,cmp);int cnt=0;
56         tot=1;
57     for(i=1;i<=n1;insert(a[i].id,cnt+n),i++)
58         if(a[i].v!=a[i-1].v||i==1)b[++cnt]=a[i].v;
59 //  for(i=1;i<=n1;i++)printf("   %lld  %d\\n",a[i].v,a[i].id);
60     s=0,t=n+cnt+1;
61     for(i=1;i<=n;i++)insert(s,i);
62     for(i=1;i<=cnt;i++)insert(i+n,t);
63     while(bfs())ans+=dfs(s,1<<23);
64     if(ans==n){
65         for(i=1;i<=n;i++)
66             for(j=last[i];j;j=e[j].pre)if(e[j].too&&!e[j].flow){
67                 ll k=b[e[j].too-n];
68                 if(x[i]+y[i]==k)printf("%d + %d = %lld\\n",x[i],y[i],k);else
69                 if(x[i]-y[i]==k)printf("%d - %d = %lld\\n",x[i],y[i],k);else
70                 if(1LL*x[i]*y[i]==k)printf("%d * %d = %lld\\n",x[i],y[i],k);
71                 break;
72             }
73     }else puts("impossible");
74     return 0;
75 }

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