CodeForces-552E. Vanya and Brackets

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/*CF e题 给定一个表达式，只添加一对括号，使得这个表达式的值最大* 由于乘号比较少，枚举括号的位置就行；* 左括号的位置一定在乘号的右边，右括号的位置一定在乘号的左边，* 这样才能使得表达式的值最大，否则移动括号一定能找到比较大的值*/#include<map>#include<vector>#include<cstdio>#include<iostream>#include<cstring>#include<string>#include<algorithm>#include<cmath>#include<stack>#include<queue>#include<set>#define inf 0x3f3f3f3f#define mem(a,x) memset(a,x,sizeof(a))using namespace std;typedef long long ll;typedef pair<int,int> pii;inline int in(){    int res=0;char c;    while((c=getchar())<'0' || c>'9');    while(c>='0' && c<='9')res=res*10+c-'0',c=getchar();    return res;}stack<ll> num;stack<ll> num2;stack<char> ch;ll calc(string & s){    while(num.size())num.pop();    while(num2.size())num2.pop();    while(ch.size())ch.pop();    int n=s.size();    bool have=0;    int k1,k2;    for(int i=0;i<n;i++)    {        if(s[i]=='(')           {               have=1;               k1=i;               ++i;               while(s[i]!=')')               {                   if(s[i]=='*')                   {                       ch.push(s[i]);                   }                   else if(s[i]>='0' && s[i]<='9')                   {                       if(ch.size() && ch.top()=='*')                       {                           ll t1 = s[i]-'0';                           ll t2 = num.top();                           num.pop();                           ch.pop();                           num.push(t1*t2);                       }                       else num.push(s[i]-'0');                   }                   ++i;               }               k2=i;               break;           }    }    ll tmp=0;    while(num.size())    {        tmp+=num.top();        num.pop();    }    string t=".";    if(have)s.replace(k1,k2-k1+1,t);    //cout<<s<<endl;    n=s.size();    for(int i=0;i<n;i++)    {        if(s[i]=='*')ch.push(s[i]);        else if((s[i]>='0' && s[i]<='9') || s[i]=='.')           {               if(ch.size() && ch.top()=='*')               {                   ll t1;                   if(s[i]!='.')t1 = s[i]-'0';                   else t1 = tmp;                   ll t2 = num.top();                   num.pop();                   ch.pop();                   num.push(t1*t2);               }               else num.push(s[i]=='.'? tmp:s[i]-'0');           }    }    ll res=0;    while(num.size())    {        res+=num.top();        //cout<<num.top()<<endl;        num.pop();    }    //cout<<"res=="<<res<<endl;    return res;}vector<int> vec;int main(){    string s,t;    cin>>s;    t=s;    vec.clear();    int n=s.size();    vec.push_back(-1);    for(int i=1;i<n;i+=2)    {        if(s[i]=='*')        {            vec.push_back(i);        }    }    vec.push_back(n);    n=vec.size();    ll ans=calc(s);    for(int i=0;i<n-1;i++)    {        for(int j=i+1;j<n;j++)        {            s=t;            s.insert(vec[i]+1,1,'(');            s.insert(vec[j]+1,1,')');            //cout<<s<<endl;            ans=max(ans,calc(s));        }    }    cout<<ans<<endl;    return 0;}
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