UVA 208 并查集+dfs

//http://acm.hust.edu.cn/vjudge/problem/19858//要先判断N与1是否联通,以及要搜索的点应该与N联通。#include <stdio.h>#include <string>#include <cstring>#include <queue>#include <algorithm>#include <functional>#include <vector>#include <sstream>#include <iomanip>#include <math.h>#include <iostream>#include <sstream>#include <time.h>#include <stack>#include <set>#include <map>#include <time.h>#include <bitset>using namespace std;const int MAX=25;int N,a,b,M;int G[MAX][MAX];int pre[MAX];bool used[MAX];int Ans[MAX],Cnt;int Find(int x){    int r=x;    while(r!=pre[r])        r=pre[r];    int i=x,j;    while(pre[i]!=r)    {        j=pre[i];        pre[i]=r;        i=j;    }    return r;}void mix(int x,int y){    int fx=Find(x),fy=Find(y);    if(fx!=fy)        pre[fy]=fx;}void dfs(int x,int l){    Ans[l]=x;    if (x==N)    {        for (int i=0;i<=l;i++)            cout<<Ans[i]<<(i==l?'\n':' ');        Cnt+=1;        return;    }    for (int i=1;i<MAX;i++)    {        if (!used[i]&&i!=x&&Find(i)==M&&G[x][i]==1)        {            used[i]=true;            dfs(i,l+1);            used[i]=false;        }    }}int main(){    cin.sync_with_stdio(false);    int cases=1;    while (cin>>N)    {        for (int i=0;i<MAX;i++)            pre[i]=i;        Cnt=0;        memset(G,0,sizeof(G));        memset(used,false,sizeof(used));        memset(Ans,0,sizeof(Ans));        cout<<"CASE "<<cases++<<":\n";        while (cin>>a>>b)        {            if (a==0&&b==0)                break;            G[a][b]=G[b][a]=1;            mix(a,b);        }        if (Find(1)==Find(N))        {            M=Find(1);            used[1]=true;            dfs(1,0);        }        cout<<"There are "<<Cnt<<" routes from the firestation to streetcorner "<<N<<".\n";    }    return 0;}