E - We Need More Bosses

CodeForces - 1000E

Your friend is developing a computer game. He has already decided how the game world should look like — it should consist of nn locations connected by mm two-waypassages. The passages are designed in such a way that it should be possible to get from any location to any other location.

Of course, some passages should be guarded by the monsters (if you just can go everywhere without any difficulties, then it's not fun, right?). Some crucial passages will be guarded by really fearsome monsters, requiring the hero to prepare for battle and designing his own tactics of defeating them (commonly these kinds of monsters are called bosses). And your friend wants you to help him place these bosses.

The game will start in location ss and end in location tt, but these locations are not chosen yet. After choosing these locations, your friend will place a boss in each passage such that it is impossible to get from ss to tt without using this passage. Your friend wants to place as much bosses as possible (because more challenges means more fun, right?), so he asks you to help him determine the maximum possible number of bosses, considering that any location can be chosen as ss or as tt.

Input

The first line contains two integers nn and mm (2≤n≤3⋅1052≤n≤3⋅105, n−1≤m≤3⋅105n−1≤m≤3⋅105) — the number of locations and passages, respectively.

Then mm lines follow, each containing two integers xx and yy (1≤x,y≤n1≤x,y≤n, x≠yx≠y) describing the endpoints of one of the passages.

It is guaranteed that there is no pair of locations directly connected by two or more passages, and that any location is reachable from any other location.

Output

Print one integer — the maximum number of bosses your friend can place, considering all possible choices for ss and tt.

Examples

Input

5 51 22 33 14 15 2

Output

2

Input

4 31 24 33 2

Output

3

题意:

给你一个无向图,让你招到一个路径,这条路径中”桥“最多。

输出最多的桥的数量。

思路:

直接用tarjan强连通缩点后建树,然后树的直径就是答案。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <vector>
#include <iomanip>
#define ALL(x) (x).begin(), (x).end()
#define sz(a) int(a.size())
#define all(a) a.begin(), a.end()
#define rep(i,x,n) for(int i=x;i<n;i++)
#define repd(i,x,n) for(int i=x;i<=n;i++)
#define pii pair<int,int>
#define pll pair<long long ,long long>
#define gbtb ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define MS0(X) memset((X), 0, sizeof((X)))
#define MSC0(X) memset((X), '\0', sizeof((X)))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define eps 1e-6
#define gg(x) getInt(&x)
#define chu(x) cout<<"["<<#x<<" "<<(x)<<"]"<<endl
using namespace std;
typedef long long ll;
ll gcd(ll a, ll b) {return b ? gcd(b, a % b) : a;}
ll lcm(ll a, ll b) {return a / gcd(a, b) * b;}
ll powmod(ll a, ll b, ll MOD) {ll ans = 1; while (b) {if (b % 2) { ans = ans * a % MOD; } a = a * a % MOD; b /= 2;} return ans;}
inline void getInt(int *p);
const int maxn = 700010;
const int inf = 0x3f3f3f3f;
/*** TEMPLATE CODE * * STARTS HERE ***/
const int MAXN = maxn;
const int MAXM = maxn; struct Edge {
int to, next;
bool cut;
} edge[MAXM];
int head[MAXN], tot;
int Low[MAXN], DFN[MAXN], Stack[MAXN], Belong[MAXN]; //Belong数组的值是1~block
int Index, top;
int block;
bool Instack[MAXN];
int bridge; void addedge(int u, int v)
{
edge[tot].to = v; edge[tot].next = head[u]; edge[tot].cut = false;
head[u] = tot++;
}
void Tarjan(int u, int pre)
{
int v;
Low[u] = DFN[u] = ++Index;
Stack[top++] = u;
Instack[u] = true;
for (int i = head[u]; i != -1; i = edge[i].next) {
v = edge[i].to;
if ( v == pre ) { continue; }
if ( !DFN[v] ) {
Tarjan(v, u);
if (Low[u] > Low[v]) { Low[u] = Low[v]; }
if (Low[v] > Low[u]) {
bridge++;
edge[i].cut = true;
edge[i ^ 1].cut = true;
}
} else if (Instack[v] && Low[u] > DFN[v]) {
Low[u] = DFN[v];
}
}
if (Low[u] == DFN[u]) {
block++;
do {
v = Stack[--top];
Instack[v] = false;
Belong[v] = block;
} while ( v != u );
}
}
void init()
{
tot = 0;
memset(head, -1, sizeof(head));
} vector<int>vec[MAXN];
// 调用lca求最近公共祖先
// ans为在U和V之间加再加一个边,剩下的桥数量。
// int ans = 0; int ans = 0;
int dist[MAXN];
int id;
int num = -1;
void dfs(int x, int pre)
{
dist[x] = dist[pre] + 1;
for (auto y : vec[x]) {
if (y != pre) {
dfs(y, x);
}
}
}
void solve(int N)
{
memset(DFN, 0, sizeof(DFN));
memset(Instack, false, sizeof(Instack));
Index = top = block = 0;
Tarjan(1, 1);
for (int i = 1; i <= block; i++) {
vec[i].clear();
}
for (int u = 1; u <= N; u++)
for (int i = head[u]; i != -1; i = edge[i].next) {
int v = edge[i].to;
if (Belong[u] != Belong[v]) {
vec[Belong[u]].push_back(Belong[v]);
}
// vec[Belong[v]].push_back(Belong[u]);
}
// repd(i, 1, block) {
// sort(ALL(vec[i]));
// vec[i].erase(unique(ALL(vec[i])), vec[i].end());
// }
dfs(1, 0);
repd(i, 1, block) {
if (dist[i] > num) {
num = dist[i];
id = i;
}
}
dfs(id, 0);
repd(i, 1, block) {
ans = max(ans, dist[i]);
}
printf("%d\n", ans - 1);
}
int n, m;
int main()
{
//freopen("D:\\common_text\\code_stream\\in.txt","r",stdin);
//freopen("D:\\common_text\\code_stream\\out.txt","w",stdout); init();
gg(n);
gg(m);
repd(i, 1, m) {
int x, y;
gg(x); gg(y);
addedge(x, y);
addedge(y, x);
}
solve(n); return 0;
} inline void getInt(int *p)
{
char ch;
do {
ch = getchar();
} while (ch == ' ' || ch == '\n');
if (ch == '-') {
*p = -(getchar() - '0');
while ((ch = getchar()) >= '0' && ch <= '9') {
*p = *p * 10 - ch + '0';
}
} else {
*p = ch - '0';
while ((ch = getchar()) >= '0' && ch <= '9') {
*p = *p * 10 + ch - '0';
}
}
}

E - We Need More Bosses CodeForces - 1000E (tarjan缩点,树的直径)的更多相关文章

  1. F - Warm up HDU - 4612 tarjan缩点 + 树的直径 + 对tajan的再次理解

    题目链接:https://vjudge.net/contest/67418#problem/F 题目大意:给你一个图,让你加一条边,使得原图中的桥尽可能的小.(谢谢梁学长的帮忙) 我对重边,tarja ...

  2. We Need More Bosses CodeForces - 1000E(缩点 建图 求桥 求直径)

    题意: 就是求桥最多的一条路 解析: 先求连通分量的个数 然后缩点建图  求直径即可 #include <bits/stdc++.h> #define mem(a, b) memset(a ...

  3. We Need More Bosses CodeForces - 1000E (无向图缩点)

    大意: 给定无向连通图, 定义两个点$s,t$个价值为切断一条边可以使$s,t$不连通的边数. 求最大价值. 显然只有桥会产生贡献. 先对边双连通分量缩点建树, 然后求直径即为答案. #include ...

  4. cf1000E We Need More Bosses (tarjan缩点+树的直径)

    题意:无向联通图,求一条最长的路径,路径长度定义为u到v必须经过的边的个数 如果把强联通分量都缩成一个点以后,每个点内部的边都是可替代的:而又因为这是个无向图,缩完点以后就是棵树,跑两遍dfs求直径即 ...

  5. codeforces GYM 100114 J. Computer Network 无相图缩点+树的直径

    题目链接: http://codeforces.com/gym/100114 Description The computer network of “Plunder & Flee Inc.” ...

  6. 4612 warm up tarjan+bfs求树的直径(重边的强连通通分量)忘了写了,今天总结想起来了。

    问加一条边,最少可以剩下几个桥. 先双连通分量缩点,形成一颗树,然后求树的直径,就是减少的桥. 本题要处理重边的情况. 如果本来就两条重边,不能算是桥. 还会爆栈,只能C++交,手动加栈了 别人都是用 ...

  7. CodeForces - 1000E :We Need More Bosses(无向图缩点+树的直径)

    Your friend is developing a computer game. He has already decided how the game world should look lik ...

  8. CF487E Tourists - Tarjan缩点 + 树剖 + multiset

    Solution 先Tarjan求出点双联通分量 并缩点. 用$multiset$维护 点双内的最小点权. 容易发现, 点双内的最小点权必须包括与它相连的割边的点权. 所以我们必须想办法来维护. 所以 ...

  9. Codeforces 734E Anton and Tree(缩点+树的直径)

    题目链接: Anton and Tree 题意:给出一棵树由0和1构成,一次操作可以将树上一块相同的数字转换为另一个(0->1 , 1->0),求最少几次操作可以把这棵数转化为只有一个数字 ...

随机推荐

  1. 写linux脚本你怎么能不知道位置参数!?

    在写shell脚本的时候,我们经常会手动设置参数,然后对我们的输入的这些参数进行处理和分析,那么这个东东到底值怎么使用的呢? 1.$n $0代表命令本身,$1-9代表接受的第1-9个参数,10以上需要 ...

  2. 【图像算法OpenCV】几何不变矩--Hu矩

    原文地址  http://blog.csdn.NET/daijucug/article/details/7535370 [图像算法OpenCV]几何不变矩--Hu矩 一 原理 几何矩是由Hu(Visu ...

  3. PHP读取TXT中文乱码的解决方法

    //$fname文件名称 if ($fname = $_FILES['nickname']['tmp_name']) { //file_get_contents() 函数把整个文件读入一个字符串中. ...

  4. shell sed 替代1

    sed -e '/-DLUA_USE_LINUX/s/-lreadline/-lreadline -lncurses/g' Makefile > tmp mv tmp Makefile 全局换- ...

  5. linux系统目录权限实践及结论

    总结测试结论:Linux目录的读.写.执行权限说明:

  6. Kafka主题体系架构-复制、故障转移和并行处理

    本文讨论了Kafka主题的体系架构,讨论了如何将分区用于故障转移和并行处理. Kafka主题,日志和分区 Kafka将主题存储在日志中.主题日志分为多个分区.Kafka将日志的分区分布在多个服务器或磁 ...

  7. [转载]Python 魔法方法详解

    据说,Python 的对象天生拥有一些神奇的方法,它们总被双下划线所包围,他们是面向对象的 Python 的一切. 他们是可以给你的类增加魔力的特殊方法,如果你的对象实现(重载)了这些方法中的某一个, ...

  8. Elastic Search对Document的搜索

    在ES中使用的重点.ES中存储的数据.核心就是为了提供全文搜索能力的.搜索功能非常重要.多练. 1 query string searchsearch的参数都是类似http请求头中的字符串参数提供搜索 ...

  9. tensorflow零起点快速入门(3)

    创造并运行数据 创造了-3到3的32条数据,然后通过sess.run获取并显示输出数据. x=tf.linspace(-3.0,3.0,32) print(x) sess=tf.Session() r ...

  10. 转SSL/TLS协议

    TLS名为传输层安全协议(Transport Layer Protocol),这个协议是一套加密的通信协议.它的前身是SSL协议(安全套接层协议,Secure Sockets Layer).这两个协议 ...