DDCC2017 Final C

DDCC2017-finalC.cpp

#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <sstream>
#include <string>
#define _repargs(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _repargs(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define mod 1000000007

#define mp make_pair
#define pb push_back
typedef long long ll;
using namespace std;
template <typename T>
inline void output(T a, int p = 0) {
    if(p) cout << fixed << setprecision(p)  << a << "\n";
    else cout << a << "\n";
}
// end of template

ll inf = 1LL << 61;
struct node {int to; ll cost;};

vector<vector<node>> G;
vector<vector<node>> rG;
vector<ll> dist;
int to = 0;
bool ok = true;
void dfs(int cur) {
    for(node n: G[cur]) {
        if(to == n.to) continue;
        if(dist[n.to] == inf) {
            dist[n.to] = dist[cur] + n.cost;
            dfs(n.to);
        }
        else {
            if(dist[n.to] != dist[cur] + n.cost) ok = false;
        }
    }
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    // source code
    int N, M;
    cin >> N >> M;
    G.resize(N);
    rG.resize(N);
    rep(i, M) {
        int a, b;
        ll c;
        cin >> a >> b >> c;
        a--;
        b--;
        G[a].pb({b, c});
        rG[b].pb({a, c});
    }
    
    rep(i, N) {
        dist.assign(N, inf);
        dist[i] = 0;
        ok = true;
        to = i;
        dfs(i);
        if(ok) {
            int cnt = 0;
            for (node n: rG[i]) {
                if(dist[n.to] + n.cost != 0) cnt++;
            }
            if(cnt <= 1) {
                output("Yes");
                return 0;
            }
        }
    }
    
    output("No");
    
    return 0;
}