12.2.2. Лабиринт знаний

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

struct edge
{
    int start, finish, cost;
};

int main()
{
    int n, m;
    cin >> n >> m;
    vector<edge>e;
    for (int i = 0; i<m; i++)
    {
        edge a;
        cin >> a.start >> a.finish >> a.cost;
        a.start--;
        a.finish--;
        e.push_back(a);
    }
    vector<int> length(n, INT_MIN);
    vector<int> p(n, -1);
    length[0] = 0;
    int x;
    for (int i = 0; i<n; i++)
    {
        x = -1;
        for (int j = 0; j<m; j++)
        if ((length[e[j].start]>INT_MIN) && (length[e[j].finish]<length[e[j].start] + e[j].cost))
        {
            length[e[j].finish] = length[e[j].start] + e[j].cost;
            p[e[j].finish] = e[j].start;
            x = 1;
        }
    }
    vector<int> path;
    int k = 0;
    for (int i = n - 1; i != -1; i = p[i])
    {
        k++;
        path.push_back(i);
        if (k>n) break;
    }
    if (length[n - 1] == INT_MIN) cout << ":(" << endl;
    else
    if ((x != -1) && ((path.back() != 0) || (path.front() != n - 1) || (k>n))) cout << ":)" << endl;
    else cout << length[n - 1] << endl;
    system("pause");
    return 0;
}