UVA-140 Bandwidth （回溯+剪枝）

# include<iostream>
# include<cstdio>
# include<string>
# include<vector>
# include<cstring>
# include<algorithm>
using namespace std;
char p[100];
vector<int>v[30],w;
int ans,vis[30],n;
string ansp;
void init()
{
    int l=strlen(p);
    int now;
    for(int i=1;i<l;++i){
        if(p[i]==‘;‘)
            continue;
        if(p[i]==‘:‘){
            now=p[i-1]-‘A‘;
            continue;
        }
        if(p[i-1]!=‘;‘){
            vector<int>::iterator it;
            it=find(v[now].begin(),v[now].end(),p[i]-‘A‘);
            if(it==v[now].end())
                v[now].push_back(p[i]-‘A‘);
            it=find(v[p[i]-‘A‘].begin(),v[p[i]-‘A‘].end(),now);
            if(it==v[p[i]-‘A‘].end())
                v[p[i]-‘A‘].push_back(now);
        }
    }
    for(int i=0;i<30;++i)
        sort(v[i].begin(),v[i].end());
    w.clear();
    vector<int>::iterator it;
    for(int i=0;i<l;++i){
        if(p[i]==‘:‘||p[i]==‘;‘)
            continue;
        it=find(w.begin(),w.end(),p[i]-‘A‘);
        if(it==w.end())
            w.push_back(p[i]-‘A‘);
    }
    sort(w.begin(),w.end());
    n=w.size();
}
int f(string app,int g,int pos)
{
    for(int i=0;i<app.size();++i){
        if(i==pos)
            continue;
        if(app[i]==g+‘A‘)
            return i;
    }
    return pos;
}
int get(string app)
{
    int res=0;
    int l=app.size();
    for(int i=0;i<l;++i){
        for(int j=0;j<v[app[i]-‘A‘].size();++j){
            int pos=f(app,v[app[i]-‘A‘][j],i);
            res=max(res,abs(pos-i));
        }
    }
    return res;
}
void dfs(int cur,int now,string ap)
{
    if(cur==n){
        if(now<ans){
            ans=now;
            ansp=ap;
        }
        return ;
    }
    if(now>=ans)
        return ;
    int l=ap.size();
    if(l>0){
        string app=ap;
        for(int i=0;i<v[ap[l-1]-‘A‘].size();++i){
            int j;
            for(j=0;j<l;++j)
                if(v[ap[l-1]-‘A‘][i]==ap[j]-‘A‘)
                    break;
            if(j>=l)
                app+=char(v[ap[l-1]-‘A‘][i]+‘A‘);
        }
        if(get(app)>=ans)
            return ;
    }
    for(int i=0;i<n;++i){
        if(vis[w[i]])
            continue;
        vis[w[i]]=1;
        dfs(cur+1,get(ap+char(w[i]+‘A‘)),ap+char(w[i]+‘A‘));
        vis[w[i]]=0;
    }
}
int main()
{
    while(scanf("%s",p))
    {
        if(p[0]==‘#‘)
            break;
        for(int i=0;i<30;++i)
            v[i].clear();
        init();
        ans=100;
        ansp.clear();
        memset(vis,0,sizeof(vis));
        dfs(0,0,"");
        int len=ansp.size();
        for(int i=0;i<len;++i)
            printf("%c ",ansp[i]);
        printf("-> %d\n",ans);
    }
    return 0;
}