代码

#include <iostream>
#include <string>
#include <vector>
using namespace std;

const int N = 1505;
int dp[N][N];

int main()
{
    for(int i = 1; i <= N - 5; i++)
    {
        for(int j = 1; j <= N - 5; j++)
        {
            dp[i][j] = 2e9;
        }
    }
	int n, m;
	cin >> n >> m;
	for(int i = 1; i <= m; i++)
	{
		int u, v, w;
		cin >> u >> v >> w;
		w = -w;
		dp[u][v] = w;
	}
	for(int k = 1; k <= n; k++)
	{
		for(int i = 1; i <= n; i++)
		{
			for(int j = 1; j <= n; j++)
			{
				dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j]);
			}
		}
	}
	cout << ((dp[1][n] == 2e9) ? -1 : (dp[1][n] * -1)) << endl;
	return 0;
}