Graph/Shortest_path/Bellman_ford.h

• View this file on GitHub
• Last update: 2025-06-07 22:39:21+07:00

Depends on

• template.h

Verified with

• Graph/test/aizu_grl_1_b_negative_cycle.test.cpp

Code

#include "../../template.h"

// if exist negative cycle d[S] = 1e18
// else return shortest path
vector<ll> negativeCycle(int S, int n, vector<vector<pii>> &g){
    vector<ll> d(n+1, 1e18);
    d[S] = 0;
    for (int i = 0; i < n - 1; i++) {
        for (int u = 0; u < n; u++) {
            for (auto [v, w] : g[u]) {
                if (d[u] != 1e18) {
                    d[v] = min(d[v], d[u]+w);
                }
            }
        }
    }
    for (int i = 0; i < n; i++) {
        for (int u = 0; u < n; u++) {
            for (auto [v, w] : g[u]) {
                if (d[u] != 1e18 && d[v] > d[u] + w) {
                    d[S] = 1e18;
                    return d;
                }
            }
        }
    }
    return d;
}

#line 2 "template.h"

#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
#define MOD (ll)(1e9+7)
#define all(x) (x).begin(),(x).end()
#define unique(x) x.erase(unique(all(x)), x.end())
#define INF32 ((1ull<<31)-1)
#define INF64 ((1ull<<63)-1)
#define inf (ll)1e18

#define vi vector<int>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second

const int mod = 998244353;

void solve();

int main(){
    ios_base::sync_with_stdio(false);cin.tie(NULL);
    // cin.exceptions(cin.failbit);
    // int t; cin >> t;
    // while(t--)
        solve();
    cerr << "\nTime run: " << 1000 * clock() / CLOCKS_PER_SEC << "ms" << '\n';
    return 0;
}
#line 2 "Graph/Shortest_path/Bellman_ford.h"

// if exist negative cycle d[S] = 1e18
// else return shortest path
vector<ll> negativeCycle(int S, int n, vector<vector<pii>> &g){
    vector<ll> d(n+1, 1e18);
    d[S] = 0;
    for (int i = 0; i < n - 1; i++) {
        for (int u = 0; u < n; u++) {
            for (auto [v, w] : g[u]) {
                if (d[u] != 1e18) {
                    d[v] = min(d[v], d[u]+w);
                }
            }
        }
    }
    for (int i = 0; i < n; i++) {
        for (int u = 0; u < n; u++) {
            for (auto [v, w] : g[u]) {
                if (d[u] != 1e18 && d[v] > d[u] + w) {
                    d[S] = 1e18;
                    return d;
                }
            }
        }
    }
    return d;
}

Back to top page