【模板】链式前向星+spfa

洛谷传送门——分糖果

博客——链式前向星

团队中一道题，数据很大，只能用链式前向星存储，spfa求单源最短路。

可做模板。

#include <cstdio>
#include <queue>
#include <cstring>
#include <algorithm>

using namespace std;

int n, p, c, ans, cnt;
long long m;
struct node
{
    int to, next;
}edge[5000001];
int dis[5000001], head[500001], x, y;
bool vis[5000001];

void spfa()
{
    int i, j;
    queue <int> q;
    memset(dis, 0x7f, sizeof(dis));
    dis[c] = 1;
    vis[c] = 1;
    q.push(c);
    while(!q.empty())
    {
        i = q.front();
        q.pop();
        vis[i] = 0;
        for(j = head[i]; j >= 0; j = edge[j].next)
         if(dis[edge[j].to] > dis[i] + 1)
         {
             dis[edge[j].to] = dis[i] + 1;
             if(!vis[edge[j].to])
             {
                 q.push(edge[j].to);
                 vis[edge[j].to] = 1;
             }
         }
    }
}

int main()
{
    int i, j;
    scanf("%d %d %d", &n, &p, &c);
    scanf("%d", &m);
    memset(head, -1, sizeof(head));
    for(i = 1; i <= p; i++)
    {
        scanf("%d %d", &x, &y);
        edge[cnt].to = y;
        edge[cnt].next = head[x];
        head[x] = cnt++;
        edge[cnt].to = x;
        edge[cnt].next = head[y];
        head[y] = cnt++;
    }
    spfa();
    for(i = 1; i <= n; i++) ans = max(ans, dis[i]);
    printf("%lld", ans + m);
    return 0;
}
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