HihoCoder #1369 : 网络流一·Ford-Fulkerson算法

1.题面

http://hihocoder.com/problemset/problem/1369

2.题意

给你一张图，求从１到n的最大流

3.思路

使用Dinic算法

4.代码

/*****************************************************************
> File Name: cpp_acm.cpp
> Author: Uncle_Sugar
> Mail: uncle_sugar@qq.com
> Created Time: Sun 02 Oct 2016 13:36:50 CST
*****************************************************************/
# include <cstdio>
# include <cstring>
# include <cctype>
# include <cmath>
# include <cstdlib>
# include <climits>
# include <iostream>
# include <iomanip>
# include <set>
# include <map>
# include <vector>
# include <stack>
# include <queue>
# include <algorithm>
using namespace std;

# define rep(i,a,b) for (i=a;i<=b;i++)
# define rrep(i,a,b) for (i=b;i>=a;i--)
# define mset(aim, val) memset((aim), (val), sizeof(aim))

template<class T>void PrintArray(T* first,T* last,char delim=' '){
for (;first!=last;first++) cout << *first << (first+1==last?'\n':delim);
}

/*
1.see the size of the input data before you select your algorithm
2.cin&cout is not recommended in ACM/ICPC
3.pay attention to the size you defined, for instance the size of edge is double the size of vertex
*/

const int debug = 1;
//# const int size = 10 + ;
const int INF = INT_MAX>>1;
typedef long long ll;

const int MAXN = 100 + 100000;
const int MAXM = 100 + 200000;

struct Edge{
int to, nxt, f;
};

struct Dinic_MaxFlow{
int head[MAXN], tot;
Edge edge[MAXM];
int level[MAXN];

void init(){
tot = 0; mset(head, -1);
}

void addedge(int from, int to, int f){
edge[tot].to = to; edge[tot].f = f;
edge[tot].nxt = head[from]; head[from] = tot++;

edge[tot].to = from; edge[tot].f = 0;
edge[tot].nxt = head[to]; head[to] = tot++;
}

bool bfs(int s, int t){
static queue<int> que;
while (!que.empty()) que.pop();
mset(level, 0);
level[s] = 1;
que.push(s);
while (!que.empty()){
int c = que.front();que.pop();
if (c == t) return true;
for (int e = head[c]; ~e; e = edge[e].nxt){
int to = edge[e].to, f = edge[e].f;
//# cout << "to = " << to << endl;
if (!level[to] && f){
level[to] = level[c] + 1;
que.push(to);
}
}
}
return false;
}

int dfs(int u, int t, int sup){
if (u == t) return sup;
int ret = 0;
for (int e = head[u]; ~e; e = edge[e].nxt){
int to = edge[e].to, f = edge[e].f;
//# cout << "to = " << to << endl;
if (level[to] == level[u] + 1 && f){
int mi = min(sup - ret, f);
int tf = dfs(to, t, mi);
edge[e].f -= tf;
edge[e^1].f += tf;
ret += tf;
if (ret == sup) return ret;
}
}
return ret;
}

int Dinic(int s, int t){
int ret = 0;
while (bfs(s, t)) ret += dfs(s, t, INF);
return ret;
}
}dinic;

int main(){
/*std::ios::sync_with_stdio(false);cin.tie(0);*/
int n, m;
while (~scanf("%d%d", &n, &m)){
dinic.init();
for (int i = 0; i < m; i++){
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
dinic.addedge(a, b, c);
//# dinic.addedge(b, a, c);
}
printf("%d\n", dinic.Dinic(1, n));
//# cout << dinic.Dinic(1, n) << endl;

}
return 0;
}