http://acm.bnu.edu.cn/v3/external/gym/101485.pdf
1 #include<bits/stdc++.h> 2 using namespace std; 3 typedef long long ll; 4 const int maxn=2502; 5 struct node 6 { 7 ll x; 8 ll y; 9 int id; 10 }a[maxn]; 11 int n; 12 ll b[maxn*3]; 13 int cnt; 14 struct Edge 15 { 16 int to; 17 int nxt; 18 int w; 19 }e[maxn*6]; 20 int tot; 21 int head[maxn]; 22 map<ll,int> mp; 23 bool vis[maxn*3]; 24 int used[maxn*3]; 25 char op[maxn]; 26 void init() 27 { 28 tot=0; 29 memset(head,-1,sizeof(head)); 30 memset(vis,false,sizeof(vis)); 31 memset(used,-1,sizeof(used)); 32 } 33 void add(int u,int v) 34 { 35 e[tot].to=v; 36 e[tot].w=1; 37 e[tot].nxt=head[u]; 38 head[u]=tot++; 39 } 40 int dfs(int u) 41 { 42 for(int i=head[u];i!=-1;i=e[i].nxt) 43 { 44 int v=e[i].to; 45 if(!vis[v]&&e[i].w) 46 { 47 vis[v]=true; 48 if(used[v]==-1||dfs(used[v])) 49 { 50 used[v]=u; 51 return 1; 52 } 53 } 54 } 55 return 0; 56 } 57 58 void output() 59 { 60 for(int i=0;i<cnt;i++) 61 { 62 if(used[mp[b[i]]]==-1) continue; 63 int id=used[mp[b[i]]]; 64 if(a[id].x+a[id].y==b[i]) op[id]='+'; 65 else if(a[id].x-a[id].y==b[i]) op[id]='-'; 66 else op[id]='*'; 67 } 68 for(int i=1;i<=n;i++) 69 { 70 printf("%lld %c %lld",a[i].x,op[i],a[i].y); 71 ll res; 72 if(op[i]=='+') res=a[i].x+a[i].y; 73 else if(op[i]=='-') res=a[i].x-a[i].y; 74 else if(op[i]=='*') res=a[i].x*a[i].y; 75 printf(" = %lld ",res); 76 } 77 } 78 int main() 79 { 80 while(~scanf("%d",&n)) 81 { 82 init(); 83 mp.clear(); 84 cnt=0; 85 for(int i=1;i<=n;i++) 86 { 87 scanf("%lld%lld",&a[i].x,&a[i].y); 88 a[i].id=i; 89 b[cnt++]=a[i].x+a[i].y; 90 b[cnt++]=a[i].x-a[i].y; 91 b[cnt++]=a[i].x*a[i].y; 92 } 93 sort(b,b+cnt); 94 cnt=unique(b,b+cnt)-b; 95 // for(int i=0;i<cnt;i++) 96 // { 97 // cout<<b[i]<<" "; 98 // } 99 // cout<<endl; 100 for(int i=0;i<cnt;i++) 101 { 102 mp[b[i]]=i+1; 103 } 104 for(int i=1;i<=n;i++) 105 { 106 ll x=a[i].x+a[i].y; 107 ll y=a[i].x-a[i].y; 108 ll z=a[i].x*a[i].y; 109 int posx=mp[x]; 110 int posy=mp[y]; 111 int posz=mp[z]; 112 // cout<<posx<<" "<<posy<<" "<<posz<<endl; 113 add(i,posx); 114 if(posy!=posx) add(i,posy); 115 if(posz!=posy && posz!=posx) add(i,posz); 116 } 117 int ans=0; 118 for(int i=1;i<=n;i++) 119 { 120 memset(vis,false,sizeof(vis)); 121 ans+=dfs(i); 122 } 123 if(ans<n) 124 { 125 puts("impossible"); 126 } 127 else 128 { 129 output(); 130 } 131 } 132 return 0; 133 }