【网络流】poj 1273 Drainage Ditches

第一次写网络流的算法，巨水的题目......利用残留网络不断的寻找增广路径就行了。

#include<iostream>#include<queue>using namespace std;bool augment(); //capacity of pipeint capacity[205][205];//previous pipeint record[1005];int n;bool checked[205];queue<int> q;int main(){int pipeNumber,maximum,minimum;int x,y,cap,tmpPre,tmpNext;while(cin>>pipeNumber>>n){for(int i=1;i<=n;i++)for(int j=1;j<=n;j++){capacity[i][j]=0;//node[i][j].capacity=0;//node[i][j].pre=-1;record[i]=-1;}for(int i=0;i<pipeNumber;i++){cin>>x>>y>>cap;//if(cap>capacity[x][y])capacity[x][y]+=cap;}maximum=0;while(augment()==true){tmpPre=record[n];tmpNext=n;minimum=999999;while(tmpPre!=-1){if(capacity[tmpPre][tmpNext]<minimum)minimum=capacity[tmpPre][tmpNext];tmpNext=tmpPre;tmpPre=record[tmpPre];}tmpPre=record[n];tmpNext=n;while(tmpPre!=-1){//更新残留网络 capacity[tmpPre][tmpNext]-=minimum;capacity[tmpNext][tmpPre]+=minimum;tmpNext=tmpPre;tmpPre=record[tmpPre];}maximum+=minimum;}cout<<maximum<<endl;}return 0;}bool augment(){bool havePath;for(int i=1;i<=n;i++)checked[i]=false;while(q.empty()==false)q.pop();checked[1]=true;q.push(1);havePath=false;//广搜寻找增广路径 while(q.empty()==false){int tmp=q.front();//找到增广路径则退出循环 if(tmp==n){havePath=true;break;}q.pop();for(int i=1;i<=n;i++){if(checked[i]==false&&capacity[tmp][i]>0){checked[i]=true;q.push(i);record[i]=tmp;}}}return havePath;}