UVA_11380_Down Went The Titanic

最新推荐文章于 2022-10-23 15:22:31 发布

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本文介绍了一个基于网络流算法的应用实例，通过定义特定的图结构来解决特定问题。该程序使用了多种C++标准库，包括容器和算法，并实现了深度优先搜索以寻找增广路径并更新流量，最终求得最大流。

#include<iostream>  
#include<sstream>  
#include<string>  
#include<vector>  
#include<list>  
#include<set>  
#include<map>
#include<stack>  
#include<queue>  
#include<algorithm>  
#include<numeric>  
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#pragma warning(disable:4996)  
using std::cin;
using std::cout;
using std::endl;
using std::stringstream;
using std::string;
using std::vector;
using std::list;
using std::pair;
using std::set;
using std::multiset;
using std::map;
using std::multimap;
using std::stack;
using std::queue;
using std::priority_queue;
const int MaxVexNum = 2000;
const int INF = 1000000000;
class Edge
{
public:
	int to, capacity, flow;
	Edge(int t, int c, int f)
	{
		to = t,capacity = c,flow = f;
	}
};
vector<pair<int, int>>direction{ {0,-1},{0,1},{1,0},{-1,0} };
class Network
{
private:
	int vexnum, edgenum, source, destination,maxflow;
	vector<vector<Edge>>adjList;
public:
	void addEdge(int from, int to, int cap)
	{
		adjList[from].push_back({ to, cap, (int)adjList[to].size() });
		adjList[to].push_back({ from, 0, (int)adjList[from].size() - 1 });
	}
	Network()
	{
		adjList.resize(MaxVexNum);
		int row, column, people;
		cin >> row >> column >> people;
		source = 0, destination = 2 * row*column + 1;
		vector<vector<char>>graph(row+1,(vector<char>)(column+1));
		for (int i = 1; i <= row; i++)
		{
			for (int j = 1; j <= column; j++)
			{
				cin >> graph[i][j];
			}
		}
		for (int i = 1; i <= row; i++)
		{
			for (int j = 1; j <= column; j++)
			{
				auto first = (i - 1)*column + j;
				auto second = first + row*column;
				switch (graph[i][j])
				{
				case '*':addEdge(source,first,1); addEdge(first, second, 1); break;
				case '.':addEdge(first, second, 1); break;
				case '@':addEdge(first, second, INF); break;
				case '#':addEdge(second, destination, people); addEdge(first, second, INF); break;
				default:break;
				}
				for (int k = 0; k < 4; k++)
				{
					int x = i + direction[k].first, y = j + direction[k].second;
					if (x >= 1 && x <= row&&y >= 1 && y <= column)
					{
						auto FIRST = (x - 1)*column + y;
						switch (graph[x][y])
						{
						case '*':addEdge(second, FIRST, 1);break;
						case '.':addEdge(second, FIRST, 1); break;
						case '@':addEdge(second, FIRST, INF); break;
						case '#':addEdge(second, FIRST, INF); break;
						default:break;
						}
					}
				}
			}
		}
	}
	int dfs(int src, int sink, int flow,vector<bool>&used)
	{
		if (src == sink)
		{
			return flow;
		}
		used[src] = true;
		for (int i = 0; i<adjList[src].size(); i++)
		{
			Edge &edge = adjList[src][i];
			if (!used[edge.to] && edge.capacity>0)
			{
				int minflow = dfs(edge.to, sink, std::min(flow, edge.capacity),used);
				if (minflow>0)
				{
					edge.capacity -= minflow;
					adjList[edge.to][edge.flow].capacity += minflow;
					return minflow;
				}
			}
		}
		return 0;
	}
	void getMaxFlow()
	{
		maxflow = 0;
		while (1)
		{
			vector<bool>used(MaxVexNum);
			int f = dfs(source, destination, INF,used);
			if (!f)
			{
				return;
			}
			maxflow += f;
		}
	}
	void print()
	{
		cout << maxflow << endl;
	}
};
int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	char ch; 
	while ((ch=cin.get())!=EOF)
	{
		ungetc(ch,stdin);
		Network network;
		network.getMaxFlow();
		network.print();
		cin.get();
	}
	return 0;
}