uva10594 Data Flow最小费用流，两个代码区别不大（我没看出区别），为什么一个对，另一个超时！！

网址：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&category=116&problem=1535&mosmsg=Submission+received+with+ID+10787830

//正确代码：
#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;
const int maxn = 110;
const int oo = 2147483647;
struct Edge
{
  int u, v, next;
  long long cost, flow;
} edge[20100];
struct Path
{
  int a, b, c;
} path[5010];
int p[maxn], prev[maxn];
long long d[maxn];
bool vis[maxn];
int tot;
queue<int> q;
void add(int u, int v, long long cost, long long flow)
{
  edge[tot].u = u;
  edge[tot].v = v;
  edge[tot].cost = cost;
  edge[tot].flow = flow;
  edge[tot].next = prev[u];
  prev[u] = tot ++;
}
void addEdge(int u, int v, long long cost, long long flow)
{
  add(u, v, cost, flow);
  add(v, u, -cost, 0);
}
bool spfa(int s, int t)
{
  int u, v;
  memset(vis, false, sizeof(vis));
  memset(p, -1, sizeof(p));
  fill(d, d + maxn, oo);
  d[s] = 0;
  vis[s] = true;
  q.push(s);
  while (!q.empty())
    {
      u = q.front();
      for (int i = prev[u]; i != -1; i = edge[i].next)
        {
          v = edge[i].v;
          if (edge[i].flow && d[u] + edge[i].cost < d[v])
            {
              d[v] = d[u] + edge[i].cost;
              p[v] = i;
              if (!vis[v])
                {
                  vis[v] = true;
                  q.push(v);
                }
            }
        }
      vis[u] = false;
      q.pop();
    }
  return d[t] != oo;
}
long long MinCostMaxFlow(int s, int t, long long amount)
{
  long long delta, flow = 0, ret = 0;

  while (spfa(s, t))
    {
      delta = oo;
      for (int i = p[t]; i != -1; i = p[edge[i].u])
        delta = min(delta, edge[i].flow);
      for (int i = p[t]; i != -1; i = p[edge[i].u])
        {
          edge[i].flow -= delta;
          edge[i ^ 1].flow += delta;
        }
      flow += delta;
      ret += delta * d[t];
    }
  if (flow == amount) return ret;
  else return -1;
}
int main()
{
  //freopen("input.txt", "r", stdin);
  //freopen("output.txt", "w", stdout);

  int N, M;
  int a, b, c;
  int amount, cap;
  long long result;
  while (scanf("%d%d", &N, &M) != EOF)
    {
      for (int i = 1; i <= M; i ++)
        scanf("%d%d%d", &path[i].a, &path[i].b, &path[i].c);
      scanf("%d%d", &amount, &cap);

      memset(prev, -1, sizeof(prev));
      tot = 0;
      addEdge(0, 1, 0, amount);
      addEdge(N, N + 1, 0, amount);

      for (int i = 1; i <= M; i ++)
        {
          addEdge(path[i].a, path[i].b, path[i].c, cap);
          addEdge(path[i].b, path[i].a, path[i].c, cap);
        }
      result = MinCostMaxFlow(0, N + 1, amount);
      if (result >= 0) printf("%lld\n", result);
      else printf("Impossible.\n");
    }
  return 0;
}



//错误代码：
#include<cstdlib>
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include <algorithm>
#include<queue>
#include<set>
#define LL long long
#define inf 2147483647
#define E 1e-7
#define M 20111
#define N 110
using namespace std;
int xx[M/4],yy[M/4];
struct Node
{
  LL w,cap;
  int u,v,next;
};
Node node[M];
int top;
int head[N];
int c[M/4];
int n,m,r,k;
LL d[N];
int p[N],s,t;
bool inq[N];
LL getflow()
{
  LL ans=0;
  int sss=0;
  queue<int> q;
  for(;;)
    {
      fill(d,d+t+1,inf);
      memset(inq,0,sizeof(inq));
      d[s]=0;
      q.push(s);
      while(!q.empty())
        {
          int u=q.front();
          q.pop();
          inq[u]=0;
          for(int i=head[u],v=node[i].v; i!=-1; i=node[i].next,v=node[i].v)
            if(node[i].cap&&d[v]>d[u]+node[i].w)
              {
                d[v]=d[u]+node[i].w;
                p[v]=i;
                if(!inq[i])
                  {
                    inq[v]=1;
                    q.push(v);
                  }
              }
        }
      if(d[t]==inf)
        break;
      int a=inf;
      for(int i=p[t]; node[i].u!=s; i=p[node[i].u])
        {
          if(node[i].cap<a)
            a=node[i].cap;
        }
      for(int i=p[t]; node[i].u!=s; i=p[node[i].u])
        {
          node[i].cap-=a;
          node[i^1].cap+=a;
        }
//        for(int i=t;i!=s;i=node[p[i]].u)
//        {
//             node[p[i]].cap-=a;
//             node[p[i]^1].cap+=a;
//        }
      sss+=a;
      ans+=a*d[t];
    }
  if(sss==r)
    {
      return ans;
    }
  return -1;
}
void init()
{
  memset(head,-1,sizeof(head));
  top=0;
}
void addnode(int a,int b,int w,int c)
{
  node[top].u=a;
  node[top].v=b;
  node[top].cap=c;
  node[top].w=w;
  node[top].next=head[a];
  head[a]=top++;
  node[top].v=a;
  node[top].u=b;
  node[top].cap=0;
  node[top].w=-w;
  node[top].next=head[b];
  head[b]=top++;
}
int main()
{
#ifndef ONLINE_JUDGE
  freopen("ex.in","r",stdin);
#endif
  while(scanf("%d%d",&n,&m)!=EOF)
    {
      for(int i=1; i<=m; i++)
        {
          scanf("%d%d%d",&xx[i],&yy[i],&c[i]);
        }
      scanf("%d%d",&r,&k);
      init();
      for(int i=1; i<=m; i++)
        {
          addnode(xx[i],yy[i],c[i],k);
          addnode(yy[i],xx[i],c[i],k);
        }
      node[top].u=0;
      node[top].v=1;
      node[top].cap=r;
      node[top].w=0;
      node[top].next=head[0];
      head[0]=top++;
      node[top].u=n;
      node[top].v=n+1;
      node[top].cap=r;
      node[top].w=0;
      node[top].next=head[n];
      head[n]=top++;
      s=0;
      t=n+1;
      LL ans=getflow();
      if(ans>0)
        printf("%lld\n",ans);
      else
        printf("Impossible.\n");
    }
  return 0;
}