wenbao与网络流

  1 const int MAXN = 20010;//点数的最大值
  2 const int MAXM = 880010;//边数的最大值
  3 const int INF = 0x3f3f3f3f;
  4 
  5 struct Node{
  6     int from, to, next;
  7     int cap;
  8 }edge[MAXM];
  9 int tol;
 10 int head[MAXN];
 11 int dep[MAXN];
 12 int gap[MAXN];//gap[x]=y :说明残留网络中dep[i]==x的个数为y
 13 
 14 int n;//n是总的点的个数，包括源点和汇点
 15 
 16 void init(){
 17     tol = 0;
 18     memset(head, -1, sizeof(head));
 19 }
 20 
 21 void addedge(int u, int v, int w){
 22     edge[tol].from = u;
 23     edge[tol].to = v;
 24     edge[tol].cap = w;
 25     edge[tol].next = head[u];
 26     head[u] = tol++;
 27     edge[tol].from = v;
 28     edge[tol].to = u;
 29     edge[tol].cap = 0;
 30     edge[tol].next = head[v];
 31     head[v] = tol++;
 32 }
 33 
 34 void BFS(int start, int end){
 35     memset(dep, -1, sizeof(dep));
 36     memset(gap, 0, sizeof(gap));
 37     gap[0] = 1;
 38     int que[MAXN];
 39     int front = 0, rear = 0;
 40     dep[end] = 0;
 41     que[rear++] = end;
 42     while(front != rear){
 43         int u = que[front++];
 44         if(front == MAXN) front = 0;
 45         for(int i = head[u]; i !=- 1; i = edge[i].next){
 46             int v = edge[i].to;
 47             if(dep[v] != -1)continue;
 48             que[rear++] = v;
 49             if(rear == MAXN) rear = 0;
 50             dep[v] = dep[u] + 1;
 51             ++gap[dep[v]];
 52         }
 53     }
 54 }
 55 
 56 int SAP(int start, int end){
 57     int res = 0;
 58     BFS(start, end);
 59     int cur[MAXN];
 60     int S[MAXN];
 61     int top = 0;
 62     memcpy(cur, head, sizeof(head));
 63     int u = start;
 64     int i;
 65     while(dep[start] < n){
 66         if(u == end){
 67             int temp = INF;
 68             int inser;
 69             for(i = 0; i < top; i++) if(temp > edge[S[i]].cap){
 70                 temp = edge[S[i]].cap;
 71                 inser = i;
 72             }
 73             for(i = 0; i < top; i++){
 74                 edge[S[i]].cap -= temp;
 75                 edge[S[i]^1].cap += temp;
 76             }
 77             res += temp;
 78             top = inser;
 79             u = edge[S[top]].from;
 80         }
 81         if(u != end && gap[dep[u]-1] == 0)//出现断层，无增广路
 82           break;
 83         for(i = cur[u]; i != -1; i = edge[i].next)
 84            if(edge[i].cap != 0 && dep[u] == dep[edge[i].to] + 1)
 85              break;
 86         if(i != -1){
 87             cur[u] = i;
 88             S[top++] = i;
 89             u = edge[i].to;
 90         }else{
 91             int min = n;
 92             for(i = head[u]; i != -1; i = edge[i].next){
 93                 if(edge[i].cap == 0) continue;
 94                 if(min > dep[edge[i].to]){
 95                     min = dep[edge[i].to];
 96                     cur[u] = i;
 97                 }
 98             }
 99             --gap[dep[u]];
100             dep[u] = min+1;
101             ++gap[dep[u]];
102             if(u != start) u = edge[S[--top]].from;
103         }
104     }
105     return res;
106 }