POJ 3228 Gold Transportation

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <cmath>
  5 #include <algorithm>
  6 #include <climits>
  7 #include <vector>
  8 #include <queue>
  9 #include <cstdlib>
 10 #include <string>
 11 #include <set>
 12 #include <stack>
 13 #define LL long long
 14 #define pii pair<int,int>
 15 #define INF 0x3f3f3f3f
 16 using namespace std;
 17 const int maxn = 210;
 18 struct arc {
 19     int to,flow,next;
 20     arc(int x = 0,int y = 0,int z = -1) {
 21         to = x;
 22         flow = y;
 23         next = z;
 24     }
 25 };
 26 arc e[maxn*maxn];
 27 int head[maxn],d[maxn],gold[maxn],store[maxn];
 28 int tot,n,m,S,T,cur[maxn],q[maxn],hd,tl;
 29 int a[maxn*maxn],b[maxn*maxn],c[maxn*maxn];
 30 void add(int u,int v,int w) {
 31     e[tot] = arc(v,w,head[u]);
 32     head[u] = tot++;
 33     e[tot] = arc(u,0,head[v]);
 34     head[v] = tot++;
 35 }
 36 void build(int mid) {
 37     memset(head,-1,sizeof(head));
 38     tot = 0;
 39     for(int i = 0; i < m; i++)
 40         if(c[i] <= mid) {
 41             add(a[i],b[i],INF);
 42             add(b[i],a[i],INF);
 43         }
 44     for(int i = 1; i <= n; i++)
 45         add(S,i,gold[i]);
 46     for(int i = 1; i <= n; i++)
 47         add(i,T,store[i]);
 48 }
 49 bool bfs() {
 50     memset(d,-1,sizeof(d));
 51     hd = tl = 0;
 52     q[tl++] = S;
 53     d[S] = 1;
 54     while(hd < tl) {
 55         int u = q[hd++];
 56         for(int i = head[u]; ~i; i = e[i].next) {
 57             if(d[e[i].to] == -1 && e[i].flow > 0) {
 58                 d[e[i].to] = d[u] + 1;
 59                 q[tl++] = e[i].to;
 60             }
 61         }
 62     }
 63     return d[T] > -1;
 64 }
 65 int dfs(int u,int low) {
 66     if(u == T) return low;
 67     int tmp = 0,a;
 68     for(int &i = cur[u]; ~i; i = e[i].next) {
 69         if(e[i].flow > 0 && d[e[i].to] == d[u] + 1 && (a = dfs(e[i].to,min(low,e[i].flow)))) {
 70             tmp += a;
 71             low -= a;
 72             e[i].flow -= a;
 73             e[i^1].flow += a;
 74             if(!low) break;
 75         }
 76     }
 77     if(!tmp) d[u] = -1;
 78     return tmp;
 79 }
 80 int dinic() {
 81     int tmp = 0;
 82     while(bfs()) {
 83         memcpy(cur,head,sizeof(head));
 84         tmp += dfs(S,INF);
 85     }
 86     return tmp;
 87 }
 88 int main() {
 89     int suma,sumb,high,low,ans;
 90     while(scanf("%d",&n),n) {
 91         suma = sumb = 0;
 92         for(int i = 1; i <= n; i++) {
 93             scanf("%d",gold+i);
 94             suma += gold[i];
 95         }
 96         for(int i = 1; i <= n; i++) {
 97             scanf("%d",store+i);
 98             sumb += store[i];
 99         }
100         scanf("%d",&m);
101         low = INF;
102         high = -1;
103         for(int i = 0; i < m; i++) {
104             scanf("%d %d %d",a+i,b+i,c+i);
105             low = min(low,c[i]);
106             high = max(high,c[i]);
107         }
108         if(suma > sumb) {
109             puts("No Solution");
110             continue;
111         }
112         ans = -1;
113         S = 0;
114         T = n + 1;
115         while(low <= high) {
116             int mid = (low + high)>>1;
117             build(mid);
118             if(dinic() >= suma) {
119                 ans = mid;
120                 high = mid - 1;
121             } else low = mid + 1;
122         }
123         if(ans > 0) printf("%d\n",ans);
124         else puts("No Solution");
125     }
126     return 0;
127 }