2021-02-26 洛谷P1996Floyd算法求解最长路

摘要：

Floyd算法求解最长路

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问题描述：

原题链接[洛谷P2196挖地雷](https://www.luogu.com.cn/problem/P2196)

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代码以及详细注释：

#include <iostream>
#include <stdio.h>
#include <vector>
#pragma warning(disable:4996)
using namespace std;

class solution {
    
    
public:
	int n;
	vector<vector<int>> cost;
	vector<vector<int>> key;
	vector<int> w;
	void floyd() {
    
    
		cin >> n;
		w.resize(n + 1);
		cost.resize(n + 1, vector<int>(n + 1,0));
		key.resize(n + 1, vector<int>(n + 1,0));

		for (int i = 1; i <= n; ++i)
		{
    
    
			cin >> w[i];
		}

		for(int i=1;i<n;++i)
			for (int j = i + 1; j <= n; ++j)
			{
    
    
				int temp;
				cin >> temp;
				cost[i][j] = temp * w[j];
			}
		for(int k=1;k<=n;++k)
			for(int i=1;i<=n;++i)
				for (int j = 1; j <= n; ++j)
				{
    
    
					if (i!=k&&k!=j&&cost[i][k]!=0 && cost[k][j]!=0 && cost[i][j] < cost[i][k] + cost[k][j])
					{
    
    
						cost[i][j] = cost[i][k] + cost[k][j];
						key[i][j] = k;
					}
				}

		int ans = 0;
		pair<int, int> res;
		for(int i=1;i<=n;++i)
			for (int j = i; j <= n; ++j)
			{
    
    
				if (ans < cost[i][j]+w[i])
				{
    
    
					ans = cost[i][j]+w[i];
					res = {
    
     i,j };
				}
			}
		outpath(res.first, res.second);
		cout << endl<< ans;
	}

	void outpath(int i, int j)
	{
    
    
		cout << i;
		out(i, j);
	}
	void out(int i, int j)
	{
    
    
		if (i == j)
			return;
		if (key[i][j] == 0)
			cout <<" "<<j;
		else
		{
    
    
			out(i, key[i][j]);
			out(key[i][j], j);
		}
	}
};

int main() {
    
    

	//freopen("in.txt", "r", stdin);
	solution s;
	s.floyd();
	return 0;
}