CodeForces 615B Longtail Hedgehog

제목: 그림에 몇 개의 연속적인 단락을 선택할 수 있고 번호를 점차적으로 늘려야 한다. 그리고 답은 이 단락의 길이*마지막 결점의 변수이다.
사고방식: 단순 DP, dp[i]=max(dp[i], dp[j]+1) 그리고 한 번 뛰면 돼요.

#include<bits/stdc++.h>
using namespace std;
const int maxn = 100005;
#define LL long long
int dp[maxn];
vector<int>e[maxn];
int cnt[maxn];
int main()
{
    int n,m;
	scanf("%d%d",&n,&m);
	for (int i = 1;i<=m;i++)
	{
		int u,v;
		scanf("%d%d",&u,&v);
		if (u<v)
			swap(u,v);
		e[u].push_back(v);
		cnt[u]++;
		cnt[v]++;
	}
	LL ans = 0;
	for (int i = 1;i<=n;i++)
	{
		for (int j = 0;j<e[i].size();j++)
			dp[i]=max(dp[i],dp[e[i][j]]);
		dp[i]++;
		ans = max(ans,1LL*dp[i]*cnt[i]);
	}
	printf("%lld
",ans);
}

Description
This Christmas Santa gave Masha a magic picture and a pencil. The picture consists of n points connected by m segments (they might cross in any way, that doesn't matter). No two segments connect the same pair of points, and no segment connects the point to itself. Masha wants to color some segments in order paint a hedgehog. In Mashas mind every hedgehog consists of a tail and some spines. She wants to paint the tail that satisfies the following conditions:

Only segments already presented on the picture can be painted;

The tail should be continuous, i.e. consists of some sequence of points, such that every two neighbouring points are connected by a colored segment;

The numbers of points from the beginning of the tail to the end should strictly increase.

Masha defines the length of the tail as the number of points in it. Also, she wants to paint some spines. To do so, Masha will paint all the segments, such that one of their ends is the endpoint of the tail. Masha defines the beauty of a hedgehog as the length of the tail multiplied by the number of spines. Masha wants to color the most beautiful hedgehog. Help her calculate what result she may hope to get.
Note that according to Masha's definition of a hedgehog, one segment may simultaneously serve as a spine and a part of the tail (she is a little girl after all). Take a look at the picture for further clarifications.
Input
First line of the input contains two integers n and m(2 ≤ n ≤ 100 000, 1 ≤ m ≤ 200 000) — the number of points and the number segments on the picture respectively.
Then follow m lines, each containing two integers ui and vi (1 ≤ ui, vi ≤ n, ui ≠ vi) — the numbers of points connected by corresponding segment. It's guaranteed that no two segments connect the same pair of points.
Output
Print the maximum possible value of the hedgehog's beauty.
Sample Input
Input

8 6
4 5
3 5
2 5
1 2
2 8
6 7

Output

9

Input

4 6
1 2
1 3
1 4
2 3
2 4
3 4

Output

12

Hint
The picture below corresponds to the first sample. Segments that form the hedgehog are painted red. The tail consists of a sequence of points with numbers 1, 2 and 5. The following segments are spines: (2, 5), (3, 5) and (4, 5). Therefore, the beauty of the hedgehog is equal to 3·3 = 9.