Problem C. Evaluation Google APAC 2017 University Test Round C

这一题现将string expression转换成一个图，在判断是否存在拓扑序就OK了。我特判了一下a<->a的环。

拓扑序初始化（将入度=0的点push进队列）过程中，要判断这些点是否都为函数。如果只是变量是不成立的，因为该变量无法被计算出。

#include<iostream>#include<stdio.h>#include<cstdio>#include<string>#include<cmath>#include<stdlib.h>#include<algorithm>#include<string.h>#include<cstring>#include<vector>#include<queue>#include<map>using namespace std;//2017 RoundC Problem C. Evaluationint T;int N;int idx;const int maxn=2010;//string lines[maxn];map<string,int>stoi;vector<int>mp[maxn];int funnode[maxn];int deg[maxn];bool ans;vector<string> findall(string line){    vector<string>vec=vector<string>();    int st=line.find("(");    int ed0=line.find(")");    if(ed0-st==1)//no para    {        return vec;    }    int ed1=line.find_first_of(",");    if(ed1==-1)//one para    {        vec.push_back(line.substr(st+1,ed0-st-1));        return vec;    }    else    {        bool exit=false;        line=line.substr(st+1);        while(!exit)        {            int ed=line.find_first_of(",");            if(ed==-1)            {                ed=line.find_first_of(")");                exit=true;                //break;            }            //cout<<"ed "<<ed<<endl;            //vec.push_back(line.substr(st+1,ed-st-1));            //cout<<line.substr(0,ed)<<endl;            vec.push_back(line.substr(0,ed));            st=line.find_first_of(",");            if(st==-1)            {                break;            }            //cout<<"st "<<st<<endl;            st++;            line=line.substr(st);            //cout<<"line "<<line<<endl;        }    }    return vec;}int getid(string node){    int nodeid=stoi[node];    //cout<<node<<" getid1 "<<nodeid<<endl;    if(nodeid==0)    {        stoi[node]=idx;        nodeid=idx;        idx++;    }    //cout<<node<<" getid2 "<<nodeid<<endl;    return nodeid;}void toporder(){    int counted=0;    queue<int>q;    for(int i=1;i<idx;i++)    {        //cout<<deg[i]<<endl;        if(deg[i]==0)        {            if(funnode[i]==1)            {                q.push(i);            }            else            {                //cout<<"here1"<<endl;                ans=false;                return;            }        }    }    if(q.empty())    {        //cout<<"here2"<<endl;        ans=false;        return;    }    while(!q.empty())    {        int u=q.front();        q.pop();        counted++;        for(int i=0;i<mp[u].size();i++)        {            int v=mp[u][i];            deg[v]--;            if(deg[v]==0)            {                q.push(v);            }        }    }    if(counted!=idx-1)    {        //cout<<"here3"<<endl;        ans=false;    }    else    {        ans=true;    }}int main(){    freopen("C-large-practice.in","r",stdin);    freopen("output.txt","w",stdout);    scanf("%d", &T);    for(int ca=1;ca<=T;ca++)    {        scanf("%d",&N);        memset(mp,0,sizeof(mp));        memset(funnode,0,sizeof(funnode));        memset(deg,0,sizeof(deg));        stoi.clear();        idx=1;        ans=true;        for(int i=0;i<N;i++)        {            string line;            cin>>line;            string left=line.substr(0,line.find("=",0));            //cout<<"l "<<left<<endl;            int leftnode=getid(left);            vector<string>right=findall(line);            if(right.size()==0)            {                string funright=line.substr(line.find("=")+1);                //cout<<"fr "<<funright<<endl;                int funrightnode=getid(funright);                mp[funrightnode].push_back(leftnode);                funnode[funrightnode]=1;                deg[leftnode]++;            }            else            {                for(int i=0;i<right.size();i++)                {                    int rightnode=getid(right[i]);                    mp[rightnode].push_back(leftnode);                    deg[leftnode]++;//indegree                    if(rightnode==leftnode)//there exists a circle a <-> a                    {                        ans=false;                    }                    //cout<<"r "<<right[i]<<endl;                }            }        }        //cout<<"idx "<<idx<<endl;        if(ans==false)        {            printf("Case #%d: BAD\n",ca);        }        else        {            toporder();            printf("Case #%d: %s\n",ca,ans==true?"GOOD":"BAD");        }        //cout<<"======"<<endl;    }    return 0;}