HDU 5353

题目大意：

相邻的朋友可以给出自己手上最多一颗糖，n个朋友形成一个环，问给的方式能否最后使所有朋友都糖的数量相同

这里我用的是网络流来做的，这里n=100000，用sap的模板可以跑过

 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 using namespace std;
 #define ll long long
 const int MAXN = ;
 const int MAXM = ;
 const int INF = 0x3f3f3f3f;
 struct Edge{
     int st , to ,  next, cap , flow;
 }edge[MAXM];

 int tol , head[MAXN] , gap[MAXN] , dep[MAXN] , cur[MAXN];

 void init(){
     tol = ;
     memset(head , -  , sizeof(head));
 }

 void add_edge(int u , int v , int w , int rw=)
 {
     edge[tol].st = u , edge[tol].to=v , edge[tol].cap = w , edge[tol].flow=;
     edge[tol].next = head[u] , head[u] = tol++;

     edge[tol].st = v , edge[tol].to = u , edge[tol].cap = rw , edge[tol].flow=;
     edge[tol].next = head[v] , head[v] = tol++;
 }

 int Q[MAXN];

 void BFS(int start , int end)
 {
     memset(dep , - , sizeof(dep));
     memset(gap ,  , sizeof(gap));
     gap[] = ;
     int front =  , rear = ;
     dep[end] = ;
     Q[rear++] = end;
     while(front != rear){
         int u  = Q[front++];
         for(int i=head[u] ; i!=- ; i=edge[i].next){
             int v = edge[i].to ;
             if(dep[v]!=-) continue;
             Q[rear++] = v;
             dep[v] = dep[u] + ;
             gap[dep[v]]++;
         }
     }
 }

 int S[MAXN];
 int sap(int start , int end , int N)
 {
     BFS(start , end);
     memcpy(cur , head , sizeof(head));
     int top=;
     int u=start;
     int ans = ;
     while(dep[start]<N)
     {
         if(u == end){
             int Min = INF;
             int inser;
             for(int i= ; i<top ; i++)
                 if(Min>edge[S[i]].cap-edge[S[i]].flow){
                     Min = edge[S[i]].cap-edge[S[i]].flow;
                     inser = i;
                 }
             for(int i= ; i<top ; i++){
                 edge[S[i]].flow+=Min;
                 edge[S[i]^].flow-=Min;
             }
             ans+=Min;
             top = inser;
             u = edge[S[top]^].to;
             continue;
         }
         bool flag = false;
         int v ;
         for(int i=cur[u] ; i!=- ; i=edge[i].next){
             v = edge[i].to;
             if(edge[i].cap-edge[i].flow && dep[v]+==dep[u]){
                 flag = true;
                 cur[u] = i;
                 break;
             }
         }
         if(flag){
             S[top++] = cur[u];
             u = v;
             continue;
         }
         int Min = N;
         for(int i=head[u] ; i!=- ; i=edge[i].next){
             if(edge[i].cap-edge[i].flow && dep[edge[i].to]<Min){
                 Min = dep[edge[i].to];
                 cur[u] = i;
             }
         }
         gap[dep[u]]--;
         if(!gap[dep[u]]) return ans;
         dep[u] = Min+;
         gap[dep[u]]++;
         if(u != start) u = edge[S[--top]^].to;
     }
     return ans;
 }
 int n , m , val[MAXN] , id[MAXN] , in[MAXN] , out[MAXN] , x,  y , fl;
 ll sum , ave;
 int main()
 {
   // freopen("in.txt" , "r" , stdin);
     int cas;
     scanf("%d",&cas);
     while(cas--){
         init();
         scanf("%d" , &n);
         sum = ;
         for(int i= ; i<=n ; i++){
             scanf("%d" , val+i);
             sum+=val[i];
         }
         bool ok = true;
         if(sum%n != ){
             ok = false;
         }
         if(!ok){
             puts("NO");
             continue;
         }
         ave = sum/n;
         for(int i= ; i<=n ; i++){
             if(abs(val[i]-ave)>) ok = false;
         }
         if(!ok){
             puts("NO");
             continue;
         }
         add_edge(n ,  ,  , );
         for(int i= ; i<=n ; i++){
             add_edge(i , i- ,  , );
         }
         int min_flow = ;
         for(int i= ; i<=n ; i++){
             if(val[i]>ave){
                 add_edge( , i , val[i]-ave);
             }
             else if(val[i]<ave){
                 add_edge(i , n+ , ave-val[i]);
                 min_flow+=ave-val[i];
             }
         }
         int flow = sap( ,n+ , n+);
       //  cout<<flow<<" "<<min_flow<<endl;
         if(flow!=min_flow) ok = false;
         if(!ok){
             puts("NO");
             continue;
         }
         int rec[MAXN][] , tot=;
         for(int i= ; i<tol ; i+=){
             if(edge[i].st>= && edge[i].to<=n){
                 /*if(edge[i].flow + edge[i^1].flow == 0){
                     cout<<edge[i].st<<" "<<edge[i].to<<endl;
                     cout<<edge[i^1].st<<" "<<edge[i^1].to<<endl;
                     continue;
                 }*/
                 if(edge[i].flow>) rec[tot][] = edge[i].st , rec[tot++][] = edge[i].to;
                 else if(edge[i^].flow>) rec[tot][] = edge[i^].st , rec[tot++][] = edge[i^].to;
             }
         }
         printf("YES\n%d\n" , tot);
         for(int i= ; i<tot ; i++) printf("%d %d\n" , rec[i][] , rec[i][]);
     }
     return ;
 }