poj 3895.Cycles of Lanes

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Cycles of Lanes

#include <vector>#include <iostream>#include <cstdio>using namespace std;#define N  5000vector<int> v[N];int vis[N];int step[N];int ans;void dfs(int x,int t){    vis[x]=1;    step[x]=t;    int i;    for(i=0;i<v[x].size();i++)    {        int k=v[x][i];        if(!vis[k])            dfs(k,t+1);        else            {                int temp=step[x]-step[k]+1;                if(temp>ans)ans=temp;            }    }}int main(){    int ca;    scanf("%d",&ca);    int n,m;    while(ca--)    {        scanf("%d%d",&n,&m);        int i,j,k;        for(i=0;i<=n;i++)        {            vis[i]=0;            v[i].clear();        }        while(m--)        {            int a,b;            scanf("%d%d",&a,&b);            v[a].push_back(b);            v[b].push_back(a);        }        ans=0;        for(i=1;i<=n;i++)        {            if(!vis[i])            {                dfs(i,1);            }        }        if(ans>=3)        printf("%d\n",ans);        else        printf("0\n");    }    return 0;}

#include <iostream>#include <string>#include <cstdio>using namespace std; int len; #define MAX 4450 int head[MAX]; int step[MAX]; struct node {     int v;     int next; } E[MAX *MAX]; int num; void init() {     num = 0;     len = 0;//note     memset(head, -1, sizeof(head));     memset(step, -1, sizeof(step)); } void add(int s, int t) {     E[num].v = t;     E[num].next = head[s];     head[s] = num++; }  void dfs(int cur, int pre) {     int i;     for(i = head[cur]; i != -1; i = E[i].next)     {         int v = E[i].v;         if(v == pre)             continue;         if(step[v] == -1)         {             step[v] = step[cur] + 1;             dfs(v, cur);         }         else         {             if(step[cur] + 1 - step[v] > len)                 len = step[cur] + 1 - step[v];         }     } } int main() {     int t;     scanf("%d", &t);     while(t--)     {         int n, m;         scanf("%d%d", &n, &m);         init();         int i;         int st, ed;         for(i = 1; i <= m; i++)         {             scanf("%d%d", &st, &ed);             add(st, ed);             add(ed, st);         }         step[1] = 0;         dfs(1, 1);         printf("%d\n", len);     } }