這道題是多校的題，比賽的時候是一道紛紛水過的板刷題。
題意：給你一些無向邊，只加一條邊，使該圖的橋最少，然後輸出最少的橋。
思路：當時大致想到思路了，就是縮點之後找出最長的鏈，然後用總的橋數減去鏈上的橋數。
也是這麼寫的，但是卡在了重邊上。。
還是接觸的題目太少了。。
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstring>
#include <queue>
#include <set>
#include <vector>
#include <stack>
#include <map>
#include <iomanip>
#define PI acos(-1.0)
#define Max 2505
#define inf 1<<28
#define LL(x) ( x << 1 )
#define RR(x) ( x << 1 | 1 )
#define REP(i,s,t) for( int i = ( s ) ; i <= ( t ) ; ++ i )
#define ll long long
#define mem(a,b) memset(a,b,sizeof(a))
#define mp(a,b) make_pair(a,b)
#define PII pair<int,int>
using namespace std;
#define M 2000005
#define N 200005
#pragma comment(linker,"/STACK:102400000,102400000")
inline void RD(int &ret) {
char c;
do {
c = getchar();
} while(c < '0' || c > '9') ;
ret = c - '0';
while((c=getchar()) >= '0' && c <= '9')
ret = ret * 10 + ( c - '0' );
}
struct edge{
int e , next , sign ;
}ed[M] ,reed[M] ;
int n , m ;
int head[N] ,num ,rehead[N] ,renum ;
int dfn[N] , low[N] ,st[N] ,inst[N] , belong[N] ;
int dp ,top ,cnt ;
int dis[N] ;
bool vis[N] ;
int bridgenum ;
void add(int s ,int e){
ed[num].e = e ;
ed[num].sign = 0 ;
ed[num].next = head[s] ;
head[s] = num ++ ;
}
void readd(int s ,int e){
reed[renum].e = e ;
reed[renum].sign = 0 ;
reed[renum].next = rehead[s] ;
rehead[s] = renum ++ ;
}
void init(){
mem(dfn, 0) ;
mem(low , 0) ;
mem(st ,0) ;
mem(belong ,0) ;
mem(head, -1) ;
num = 0 ;
dp = 0 ;
top = 0 ;
cnt = 0 ;
mem(rehead,-1) ;
renum = 0 ;
bridgenum = 0 ;
}
void tarjan(int now ,int fa){
dfn[now] = low[now] = ++ dp ;
st[top ++ ] = now ;
inst[now] = 1 ;
for (int i = head[now] ; ~i ; i = ed[i].next ){
if(ed[i].sign)continue ;
ed[i].sign = ed[i ^ 1].sign = 1 ;
int e = ed[i].e ;
if(!dfn[e]){
tarjan(e , now) ;
low[now] = min(low[now] ,low[e]) ;
if(dfn[now] < low[e]){
bridgenum ++ ;
}
}
else if(inst[e]){
low[now] = min(low[now] , dfn[e]) ;
}
}
if(low[now] == dfn[now]){
int xx ;
cnt ++ ;
do{
xx = st[-- top] ;
inst[xx] = 0 ;
belong[xx] = cnt ;
}while(xx != now) ;
}
}
void build(){
for (int i = 1 ; i <= n ; i ++ ){
dp = 0 ,top = 0 ;
if(!dfn[i]){
tarjan(i ,-1) ;
}
}
for (int i = 1 ; i <= n ; i ++ ){
for (int j = head[i] ; ~j ; j = ed[j].next ){
int e = ed[j].e ;
if(belong[i] == belong[e])continue ;
readd(belong[i] , belong[e]) ;
readd(belong[e] ,belong[i]) ;
}
}
}
queue<int>qe ;
int pos ;
int bfs(int s){
while(!qe.empty())qe.pop() ;
dis[s] = 0 ;
mem(vis , 0) ;
vis[s] = 1 ;
qe.push(s) ;
int ans = 0 ;
while(!qe.empty()){
int temp = qe.front() ;
qe.pop() ;
for (int i = rehead[temp] ; ~i ; i = reed[i].next){
int e = reed[i].e ;
if(!vis[e]){
dis[e] = dis[temp] + 1 ;
vis[e] = 1 ;
qe.push(e) ;
if(ans < dis[e]){
ans = dis[e] ;
pos = e ;
}
}
}
}
return ans ;
}
int main() {
while(scanf("%d%d",&n,&m) , (n + m)){
init() ;
while(m -- ){
int a , b ;
RD(a) ;RD(b) ;
add(a , b) ;
add(b , a) ;
}
build() ;
bfs(1) ;
int now = bfs(pos) ;
printf("%d\n",bridgenum - now) ;
}
return 0 ;
}
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstring>
#include <queue>
#include <set>
#include <vector>
#include <stack>
#include <map>
#include <iomanip>
#define PI acos(-1.0)
#define Max 2505
#define inf 1<<28
#define LL(x) ( x << 1 )
#define RR(x) ( x << 1 | 1 )
#define REP(i,s,t) for( int i = ( s ) ; i <= ( t ) ; ++ i )
#define ll long long
#define mem(a,b) memset(a,b,sizeof(a))
#define mp(a,b) make_pair(a,b)
#define PII pair<int,int>
using namespace std;
#define M 2000005
#define N 200005
#pragma comment(linker,"/STACK:102400000,102400000")
inline void RD(int &ret) {
char c;
do {
c = getchar();
} while(c < '0' || c > '9') ;
ret = c - '0';
while((c=getchar()) >= '0' && c <= '9')
ret = ret * 10 + ( c - '0' );
}
struct edge{
int e , next , sign ;
}ed[M] ,reed[M] ;
int n , m ;
int head[N] ,num ,rehead[N] ,renum ;
int dfn[N] , low[N] ,st[N] ,inst[N] , belong[N] ;
int dp ,top ,cnt ;
int dis[N] ;
bool vis[N] ;
int bridgenum ;
void add(int s ,int e){
ed[num].e = e ;
ed[num].sign = 0 ;
ed[num].next = head[s] ;
head[s] = num ++ ;
}
void readd(int s ,int e){
reed[renum].e = e ;
reed[renum].sign = 0 ;
reed[renum].next = rehead[s] ;
rehead[s] = renum ++ ;
}
void init(){
mem(dfn, 0) ;
mem(low , 0) ;
mem(st ,0) ;
mem(belong ,0) ;
mem(head, -1) ;
num = 0 ;
dp = 0 ;
top = 0 ;
cnt = 0 ;
mem(rehead,-1) ;
renum = 0 ;
bridgenum = 0 ;
}
void tarjan(int now ,int fa){
dfn[now] = low[now] = ++ dp ;
st[top ++ ] = now ;
inst[now] = 1 ;
for (int i = head[now] ; ~i ; i = ed[i].next ){
if(ed[i].sign)continue ;
ed[i].sign = ed[i ^ 1].sign = 1 ;
int e = ed[i].e ;
if(!dfn[e]){
tarjan(e , now) ;
low[now] = min(low[now] ,low[e]) ;
if(dfn[now] < low[e]){
bridgenum ++ ;
}
}
else if(inst[e]){
low[now] = min(low[now] , dfn[e]) ;
}
}
if(low[now] == dfn[now]){
int xx ;
cnt ++ ;
do{
xx = st[-- top] ;
inst[xx] = 0 ;
belong[xx] = cnt ;
}while(xx != now) ;
}
}
void build(){
for (int i = 1 ; i <= n ; i ++ ){
dp = 0 ,top = 0 ;
if(!dfn[i]){
tarjan(i ,-1) ;
}
}
for (int i = 1 ; i <= n ; i ++ ){
for (int j = head[i] ; ~j ; j = ed[j].next ){
int e = ed[j].e ;
if(belong[i] == belong[e])continue ;
readd(belong[i] , belong[e]) ;
readd(belong[e] ,belong[i]) ;
}
}
}
queue<int>qe ;
int pos ;
int bfs(int s){
while(!qe.empty())qe.pop() ;
dis[s] = 0 ;
mem(vis , 0) ;
vis[s] = 1 ;
qe.push(s) ;
int ans = 0 ;
while(!qe.empty()){
int temp = qe.front() ;
qe.pop() ;
for (int i = rehead[temp] ; ~i ; i = reed[i].next){
int e = reed[i].e ;
if(!vis[e]){
dis[e] = dis[temp] + 1 ;
vis[e] = 1 ;
qe.push(e) ;
if(ans < dis[e]){
ans = dis[e] ;
pos = e ;
}
}
}
}
return ans ;
}
int main() {
while(scanf("%d%d",&n,&m) , (n + m)){
init() ;
while(m -- ){
int a , b ;
RD(a) ;RD(b) ;
add(a , b) ;
add(b , a) ;
}
build() ;
bfs(1) ;
int now = bfs(pos) ;
printf("%d\n",bridgenum - now) ;
}
return 0 ;
}
