D. Subway
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
A subway scheme, classic for all Berland cities is represented by a set of n stations connected by n passages, each of which connects exactly two stations and does not pass through any others. Besides, in the classic scheme one can get from any station to any other one along the passages. The passages can be used to move in both directions. Between each pair of stations there is no more than one passage.
Berland mathematicians have recently proved a theorem that states that any classic scheme has a ringroad. There can be only one ringroad. In other words, in any classic scheme one can find the only scheme consisting of stations (where any two neighbouring ones are linked by a passage) and this cycle doesn't contain any station more than once.
This invention had a powerful social impact as now the stations could be compared according to their distance from the ringroad. For example, a citizen could say "I live in three passages from the ringroad" and another one could reply "you loser, I live in one passage from the ringroad". The Internet soon got filled with applications that promised to count the distance from the station to the ringroad (send a text message to a short number...).
The Berland government decided to put an end to these disturbances and start to control the situation. You are requested to write a program that can determine the remoteness from the ringroad for each station by the city subway scheme.
Input
The first line contains an integer n (3 ≤ n ≤ 3000), n is the number of stations (and trains at the same time) in the subway scheme. Then nlines contain descriptions of the trains, one per line. Each line contains a pair of integers xi, yi (1 ≤ xi, yi ≤ n) and represents the presence of a passage from station xi to station yi. The stations are numbered from 1 to n in an arbitrary order. It is guaranteed that xi ≠ yi and that no pair of stations contain more than one passage. The passages can be used to travel both ways. It is guaranteed that the given description represents a classic subway scheme.
Output
Print n numbers. Separate the numbers by spaces, the i-th one should be equal to the distance of the i-th station from the ringroad. For the ringroad stations print number 0.
Examples
input
Copy
4 1 3 4 3 4 2 1 2
output
Copy
0 0 0 0
input
Copy
6 1 2 3 4 6 4 2 3 1 3 3 5
output
Copy
0 0 0 1 1 2
一、原题地址
二、大致题意
给出n表示有n个点，然后再给出n条双向的边，询问图上的每个点点到达环的最小距离是多少。
三、大致思路
n个点n条边，所以肯定就一个环。
所以理论上只需要找到那个环，环上的点答案都是0，然后再从环上的点向外搜索就可以跑出环外面点的答案了。
如何标记出环呢，首先读入后度数为1的点肯定不在环上，所以我们可以从它们出发，去掉它们度数的影响（即与它相连的点度数减1 ），如果此时又出现了度为1的点，那么我们就再把这个新的点重复上面的操作。
这样做的正确性：首先环上的点一开始不会被加入到搜索的队列中，那么它们度数的减少就只能靠周围的点传递过来，但是即使传递过来使得环上的点度数减少，这个减少后的值也不会低于2，所以这些点永远不会进入队列（即永远不会被更新）。
四、丑陋代码
#include<iostream>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<vector>
#include<set>
#include<map>
#include<string>
#include<stack>
#include<bitset>
using namespace std;
#define PI 3.14159265
const int inf=0x3f3f3f3f;
typedef long long LL;
typedef unsigned long long ull;
int n,ind[3005],ans[3005];
vector<int>e[3005];
bool col[3005];
void read()
{
scanf("%d",&n);
for(int i=1;i<=n;i++)ind[i]=0;
for(int i=1;i<=n;i++)
{
int u,v;
scanf("%d %d",&u,&v);
e[u].push_back(v);
e[v].push_back(u);
ind[u]++;ind[v]++;
}
}
void Color()
{
queue<int>q;
for(int i=1;i<=n;i++)
{
col[i]=false;
if(ind[i]==1)
{
q.push(i);col[i]=true;
}
}
while(!q.empty())
{
int t=q.front();q.pop();
for(int i=0;i<e[t].size();i++)
{
int to =e[t][i];
if(!col[to])
{
ind[to]--;
if(ind[to]<=1)
{
q.push(to);col[to]=true;
}
}
}
}
}
void DFS(int nx,int pr,int step)
{
ans[nx]=step;
for(int i=0;i<e[nx].size();i++)
{
int to =e[nx][i];
if(to!=pr&&col[to])
{
DFS(to,nx,step+1);
}
}
}
int main()
{
read();
Color();
for(int i=1;i<=n;i++)
{
if(!col[i])DFS(i,-1,0);
}
for(int i=1;i<=n;i++)printf("%d ",ans[i]);
return 0;
}