用拓扑排序 各种数据都过了 死活wa
#include<bits/stdc++.h> #include<iostream> #include<cstring> #include<cstdio> using namespace std; //input by bxd #define rep(i,a,b) for(int i=(a);i<=(b);i++) #define repp(i,a,b) for(int i=(a);i>=(b);--i) #define RI(n) scanf("%d",&(n)) #define RII(n,m) scanf("%d%d",&n,&m) #define RIII(n,m,k) scanf("%d%d%d",&n,&m,&k) #define RS(s) scanf("%s",s); #define ll long long #define pb push_back #define REP(i,N) for(int i=0;i<(N);i++) #define CLR(A,v) memset(A,v,sizeof A) ////////////////////////////////// #define inf 0x3f3f3f3f const int N=10000+5; const int M=2*N; int head[M],pos; struct Edge { int nex,to; }edge[M]; void add(int a,int b) { edge[++pos].nex=head[a]; head[a]=pos; edge[pos].to=b; } int tot,ind,cnt,Stack[N],dfn[N],low[N],vis[N],belong[N],node[N],peo[N],in[N]; int n,m; vector<int>G[N]; void init() { pos=tot=ind=cnt=0; CLR(Stack,0); CLR(in,0); CLR(peo,0); CLR(head,0); CLR(vis,0); CLR(dfn,0); CLR(low,0); } void tarjan(int x) { dfn[x]=low[x]=++tot; Stack[++ind]=x; vis[x]=1; for(int i=head[x];i;i=edge[i].nex) { int v=edge[i].to; if(!dfn[v]) { tarjan(v); low[x]=min(low[x],low[v]); } else if(vis[v]) low[x]=min(low[x],low[v]); } if(dfn[x]==low[x]) { cnt++;int v; do { v=Stack[ind--]; vis[v]=0; belong[v]=cnt; peo[cnt]+=node[v]; } while(x!=v); } } int main() { while(~RII(n,m)) { int sum=0; rep(i,1,n)RI(node[i]),sum+=node[i]; rep(i,1,m) { int a,b;RII(a,b); a++;b++; add(a,b); add(b,a); } cnt=0; rep(i,1,n) if(!dfn[i])tarjan(i); int num=0; rep(i,1,n) { int u=belong[i]; for(int j=head[i];j;j=edge[j].nex) { int v=belong[ edge[j].to ]; if(u!=v) { int ok=1; if(G[u].size()) rep(i,0,G[u].size()-1) { if(G[u][i]==v)ok=0; } if(ok)G[u].pb(v),in[v]++,num++; } } } printf("cnt=%d num=%d\n",cnt,num); if(num!=cnt-1||cnt==1) printf("impossible\n"); else { queue<int>q; CLR(node,0); rep(i,1,cnt) if(!in[i]) { node[i]=peo[i]; q.push(i); } int ans=inf; while(!q.empty()) { int u=q.front();q.pop(); ans=min(ans,abs( sum-node[u]-node[u] )); if(G[u].size()) rep(i,0,G[u].size()-1) { int v=G[u][i]; node[v]+=node[u]; ans=min(ans,abs( sum-node[v]-node[v] )); if(--in[v]==0) { node[v]+=peo[v]; ans=min(ans,abs( sum-node[v]-node[v] )); q.push(v); } } } printf("%d\n",ans); } rep(i,1,cnt) G[i].clear(); init(); } return 0; }
原来是双联通分量 顶不住了 待补
贴上大佬代码：
#include<cstdio> #include<stack> #include<cstring> #include<algorithm> using namespace std; const int maxn = 10005; const int maxm = 20005; int n,m; int va[maxn]; struct node { int to; int next; node(){} node(int a,int b):to(a),next(b){} }edge[maxm<<1],tree[maxm<<1]; int head[maxn],dfn[maxn],low[maxn],belong[maxn],thead[maxn],ans[maxn]; int tot,ti,coun,ttot,res,people; stack<int>s; void add_edge(int u,int v) { edge[tot] = node(v,head[u]); head[u] = tot++; edge[tot] = node(u,head[v]); head[v] = tot++; } void tarjan(int u,int fa) { dfn[u] = ++ti; low[u] = ti; s.push(u); int flag = 0; for(int i=head[u];i!=-1;i=edge[i].next) { int v = edge[i].to; if(v==fa&&flag==0){flag = 1;continue;} if(!dfn[v]){ tarjan(v,u); low[u] = min(low[u],low[v]); }else if(belong[v]==-1) low[u] = min(low[u],dfn[v]); } if(low[u]==dfn[u]) { int y; coun++; do{ y = s.top(); s.pop(); ans[coun] += va[y]; belong[y] = coun; }while(y!=u); } } int cbh(int u,int fa) { int sum = ans[u]; dfn[u] = 1; for(int i=thead[u];i!=-1;i=tree[i].next) { int v = tree[i].to; if(v==fa||dfn[v]) continue; sum+=cbh(v,u); } res = min(res,abs(2*sum-people)); return sum; } int main() { int u,v; while(scanf("%d%d",&n,&m)!=EOF) { people = 0; for(int i=0;i<n;i++) scanf("%d",&va[i]),people+=va[i]; tot = 0; memset(head,-1,sizeof(head)); for(int i=0;i<m;i++) { scanf("%d%d",&u,&v); add_edge(u,v); } memset(dfn,0,sizeof(dfn)); memset(low,0,sizeof(low)); memset(ans,0,sizeof(ans)); memset(belong,-1,sizeof(belong)); coun = 0;ti = 0; tarjan(0,0); if(coun==1){printf("impossible\n");continue;} // printf("%d\n",coun); ttot = 0; memset(thead,-1,sizeof(thead)); memset(dfn,0,sizeof(dfn)); for(int i=0;i<n;i++) { for(int j=head[i];j!=-1;j=edge[j].next) { v = edge[j].to; if(belong[i]!=belong[v]) { tree[ttot] = node(belong[v],thead[belong[i]]); thead[belong[i]] = ttot++; } } } res = 0xfffffff; cbh(1,0); printf("%d\n",res); } return 0; }
原文：https://www.cnblogs.com/bxd123/p/10800039.html
