HDU 3549 Flow Problem 最大流 最小增广路 EK算法 传说中的入门算法

题目描述

Network flow is a well-known difficult problem for ACMers. Given a graph, your task is to find out the maximum flow for the weighted directed graph.

Input:

The first line of input contains an integer T, denoting the number of test cases.
For each test case, the first line contains two integers N and M, denoting the number of vertexes and edges in the graph. (2 <= N <= 15, 0 <= M <= 1000)
Next M lines, each line contains three integers X, Y and C, there is an edge from X to Y and the capacity of it is C. (1 <= X, Y <= N, 1 <= C <= 1000)

Output:

For each test cases, you should output the maximum flow from source 1 to sink
N.

因为两个点有多条边的情况。需要全部加起来。

直接上模板。。

#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>

#include <iostream>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <utility>

#include <cstring>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <string>
using namespace std;

#define inf 0x3f3f3f3f
#define MAXN 1005
#define clr(x,k) memset((x),(k),sizeof(x))
#define cpy(x,k) memcpy((x),(k),sizeof(x))
#define Base 10000

typedef vector<int> vi;
typedef stack<int> si;
typedef vector<string> vs;
#define sz(a) int((a).size())
#define pb push_back
#define all(c) (c).begin(),(c).end()
#define rep(i,n) for(int i = 0;i < n;++i)
#define foreach(it,c) for(vi::iterator it = (c).begin();it != (c).end();++it)

#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))
int Map[MAXN][MAXN],n,m,p[MAXN]; //map:邻接数组；n:点数；p:前驱数组
void init(){
clr(Map,0);
for(int i = 0,a,b,c;i < m;i++){
scanf("%d %d %d",&a,&b,&c);
Map[a][b] += c; //存在多重边
}
}
bool EK_Bfs(int start,int end){
queue <int>que; //宽度悠闲搜索队列
int flag[MAXN];
clr(flag,0);
clr(p,-1);
que.push(start);
flag[start]=true;
while(!que.empty()){
int e = que.front();
if(e==end) //当队头弹到终点时，即可判定增广路存在
return true;
que.pop();
for(int i= 1;i <=n;i++){
if(Map[e][i]&&!flag[i]){
flag[i] = 1;
p[i]=e;
que.push(i);
}
}
}
return false;
}
int KM_Max_Flow(int start,int end){
int u,flow_ans=0,mn;
while(EK_Bfs(start,end)){
mn = inf;
u = end;
while(p[u]!=-1){
mn = min(mn,Map[p[u]][u]);
u = p[u];
}
flow_ans+=mn;
u=end;
while(p[u]!=-1){
Map[p[u]][u]-=mn;
Map[u][p[u]]+=mn;
u=p[u];
}
}
return flow_ans;
}
int main(){
//freopen("3594.in","r",stdin);
int t,tt=0;
scanf("%d",&t);
while(t--){
scanf("%d %d",&n,&m);
init();
printf("Case %d: %d\n",++tt,KM_Max_Flow(1,n));
}
return 0;
}