poj Drainage Ditches

模版题，很多人A.模版：http://blog.csdn.net/rookie_algo/article/details/7803313

#include<iostream>using namespace std;const int inf = 0x7fffffff;const int MAXN = 210;const int MAXM = MAXN*MAXN;int map[MAXN][MAXN];int dis[MAXN];int queue[MAXM];int bef[MAXN];int num[MAXN];void set_dis(int end){int top(0),base(0);memset(dis,-1,sizeof(dis));memset(num,0,sizeof(num));queue[top++] = end;dis[end]=0;num[0] = 1;while(top!=base){int pre = queue[base++];for(int i=end-1;i!=0;i--){if(dis[i] != -1 || map[i][pre] == 0)continue;dis[i] = dis[pre]+1;queue[top++] = i;num[dis[i]]++;}}}int cmp(int x,int y){if(x<y)return x;return y;}int remark(int n,int a){int tmp=inf;    for(int i=1;i!=n+1;i++)if(map[a][i]!=0&&dis[i]>=0)tmp=cmp(tmp,dis[i]+1);    if(tmp==inf)tmp=n;    return tmp;}int SAP(int n,int s){int j,a = s;int flow(0);memset(bef,-1,sizeof(bef));while(dis[s]<n){for(j=1;j!=n+1;j++){if(map[a][j]>0&&dis[a]-1==dis[j]){break;}}if(j<=n){bef[j] = a;a = j;if(a==n){int i = n,max(inf);while(bef[i]!=-1){max = cmp(max,map[bef[i]][i]);i = bef[i];}i = n;while(bef[i]!=-1){map[bef[i]][i]-=max;map[i][bef[i]]+=max;i = bef[i];}flow+=max;a=s;}}else{int x = remark(n,a);num[x]++;num[dis[a]]--;            if(num[dis[a]]==0)return flow;//间隙优化 gap            dis[a]=x;            if(a!=s)a=bef[a]; }}return flow;}int main(){int e,n;//cout<<inf<<endl;while(cin>>e>>n){memset(map,0,sizeof(map));while(e--){int a,b,w;cin>>a>>b>>w;map[a][b] += w;}set_dis(n);cout<<SAP(n,1)<<endl;}return 0;}