#72-【Dinic模板*2】Total flow

Description

Input

第1行输入N，之后N行每行描述一条水管，前两个英文字母表示水管的两端（大小写字母是不一样的），后一个整数表示水管的流量，流量不会超过1000.

 

Output

 一个整数，表示总流量．

Sample Input

5
A B 3
B C 3
C D 5
D Z 4
B Z 6

Sample Output

3

真·模板题

代码：

#include <iostream> // 模板就不用说了
#include <cstring>
#include <queue>

#define SIZE 501
#define INF 2e+09

using namespace std;

struct edge
{
	int to, cap, reverse;
};

vector<edge> graph[SIZE];
int depth[SIZE];

bool bfs(void)
{
	int u, i, v;
	queue<int> q;
	
	memset(depth, -1, sizeof (depth));
	depth['A'] = 0;
	q.push('A');
	while (!q.empty())
	{
		u = q.front();
		if (u == 'Z')
		{
			return true;
		}
		q.pop();
		for (i = 0; i < graph[u].size(); ++i)
		{
			v = graph[u][i].to;
			if ((graph[u][i].cap) && (depth[v] == -1))
			{
				depth[v] = depth[u] + 1;
				q.push(v);
			}
		}
	}
	
	return false;
}

int dfs(int u, int flow)
{
	int i, v, ret = 0, delta;
	
	if ((!flow) || (u == 'Z'))
	{
		return flow;
	}
	for (i = 0; i < graph[u].size(); ++i)
	{
		edge &temp = graph[u][i];
		v = temp.to;
		if ((depth[v] == depth[u] + 1) && (temp.cap > 0))
		{
			delta = dfs(v, min(flow - ret, temp.cap));
			if (delta > 0)
			{
				ret += delta;
				temp.cap -= delta;
				graph[v][temp.reverse].cap += delta;
				if (ret == flow)
				{
					return ret;
				}
			}
		}
	}
	
	return ret;
}

int dinic(void) // 日常Dinic
{
	int ret = 0, delta;
	
	while (bfs())
	{
		delta = dfs('A', INF);
		if (!delta)
		{
			return ret;
		}
		ret += delta;
	}
	
	return ret;
}

int main(int argc, char** argv)
{
	int m, cap;
	char u, v;
	
	scanf("%d", &m);
	while (m--)
	{
		cin >> u >> v; // 不知道为什么scanf字符会出问题,只得用cin输入
		scanf("%d", &cap);
		graph[u].push_back({v, cap, graph[v].size()});
		graph[v].push_back({u, 0, graph[u].size() + 1});
	}
	
	printf("%d", dinic());
	
	return 0;
}