CodeForces615B-Longtail Hedgehog-dp/图

记忆化数组记录从这个点的最长下降序列，然后乘以这个点的度，就是ans，维护即可。

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

using namespace std;

const int maxn = 1e5+10;
const int maxm = 4e5+100;
int N,M;

struct Edge{
    int to,next;
}edge[maxm];

int NE,head[maxn],mem[maxn],chd[maxn];
long long ans;

int add_edge(int u,int v)
{
    edge[NE].to = v;
    edge[NE].next = head[u];
    head[u] = NE++;
    chd[u]++;

    edge[NE].to = u;
    edge[NE].next = head[v];
    head[v] = NE++;
    chd[v]++;
}

long long dfs(int u)
{
    if(mem[u] != -1) {ans = max((long long)chd[u]*mem[u],ans);return mem[u];}
    mem[u] = 1;
    for(int i=head[u];~i;i=edge[i].next)
    {
        int v = edge[i].to;
        if(v > u) continue;
        mem[u] = max((long long)mem[u],dfs(v)+1);
    }

    ans = max((long long)mem[u] * chd[u],ans);
    return mem[u];
}

int main()
{
    scanf("%d%d",&N,&M);
    memset(head,-1,sizeof head);
    memset(mem,-1,sizeof mem);

    for(int i=0,u,v;i<M;i++)
    {
        scanf("%d%d",&u,&v);
        add_edge(u,v);
    }

    for(int i=1;i<=N;i++) dfs(i);


    printf("%I64d\n",ans);
}