差分约束模板

典型的 $x_u - x_v <= y$ 形式

#include<iostream>
#include<cstring>
#include<queue>
#define maxn 50007
using namespace std;
struct edge {
    int to, val, nxt;
}g[maxn];
int n, m, cnt, dis[maxn], hd[maxn], sum[maxn];
bool vis[maxn]; queue<int> q;
void add(int u, int v, int w)
{
    g[++cnt].val = w;
    g[cnt].to = v;
    g[cnt].nxt = hd[u];
    hd[u] = cnt;
}
bool spfa()
{
    memset(dis, 80, sizeof(dis));
    memset(vis, 0, sizeof(vis));
    dis[0] = 0, vis[0] = true; 
    q.push(0), ++sum[0];
    while (!q.empty())
    {
        int u = q.front();
        q.pop();
        vis[u] = false;
        for (int i = hd[u]; i; i = g[i].nxt)
        {
            int v = g[i].to;
            if (dis[v] > dis[u] + g[i].val)
            {
                dis[v] = dis[u] + g[i].val;
                if (!vis[v])
                {
                    vis[v] = true;
                    q.push(v);
                    if (++sum[v] >= n + 1)
                        return false;
                }
            }
        }
    }
    return true;
}
int main(void)
{
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);  
    cin >> n >> m;
    for (int i = 1, u, v, w; i <= m; i++)
    {
        cin >> u >> v >> w;
        add(v, u, w);
    }
    for (int i = 1; i <= n; i++)
        add(0, i, 0);
    if (spfa())
        for (int i = 1; i <= n; i++)
            cout << dis[i] << ' ';
    else
        cout << "NO" << '\n';
    return 0;
}