Codeforces Round #338 (Div. 2) B. Longtail Hedgehog 记忆化搜索/树DP

B. Longtail Hedgehog

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:

1. Only segments already presented on the picture can be painted;
2. 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;
3. 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 test(s)

input

8 64 53 52 51 22 86 7

output

9

input

4 61 21 31 42 32 43 4

output

12

Note

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.

题意：给你n个点m条边，让你找一条最长链，输出最大 的  链长度*与相连链尾节点数

题解：我们记忆花爆搜最长链，记录每个点开始所能走到的最长长度就好

　　　　注意会爆int

#include<bits/stdc++.h>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
using namespace std ;
typedef long long ll;

const int N = 1010000 ;
vector<ll  >G[N];
ll n,m,no,a,b,sum,last,dp[N];
ll dfs(ll x,ll s) {
    if(dp[x]) return dp[x];
    ll mm = 0;
    for(int i=0;i<G[x].size();i++) {
        if(G[x][i] < x) {
            mm = max(dfs(G[x][i],s+1),mm);
        }
    }
    return dp[x] = mm + 1;
}
int main () {
    scanf("%I64d%I64d",&n,&m);
    for(int i=1;i<=m;i++) {
        scanf("%I64d%I64d",&a,&b);
        G[a].push_back(b);
        G[b].push_back(a);
    }
   ll mm = 0;
     ll A = 0;
     ll nn  =  0;
     for(int i=n;i>=1;i--) {
        sum = G[i].size();
        mm = dfs(i,1);
        A = max(A,sum*mm);
     }
    printf("%I64d\n",A);
    return 0;
}

daima