ZOJ 3654 Letty's Math Class 模拟 难度:0

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=4844

题意:给你一个只包含中括号和正整数,+,-,结果在longlong范围内的公式和两个备选答案,

如果答案中有9,第一个是9选A,否则选B

否则,如果第一个是正确答案,输出B,否则输出A

#include <cstdio>

#include <iostream>

#include <cstring>

#include <cctype>

#define clr(x,y) memset(x, y, sizeof x)

#include <cmath>

using namespace std;

const int maxn=2e3+3;

typedef long long ll;

char maz[maxn];



long long read(int& head){

    //printf("read start from %d ",head);

    long long ans=0;

    while(isalnum(maz[head])){

        ans*=10;

        ans+=maz[head]-'0';

        head++;

    }

   // printf("end at %d ans = %lld\n",head,ans);

    return ans;

}

typedef pair<long long ,int > p;

p calc(int st){

    long long ans=0;

    int cnt=1,ind =st;

    for(;maz[ind]!=0&&maz[ind]!=']';){

        if(maz[ind]=='-'){

            cnt=-1;

            ind ++;

            //printf("calc ind %d cnt -1\n",ind);

        }

        else if(maz[ind]=='+'){

            ind++;

        }

        else if(isalnum(maz[ind])){

            ans+=cnt*read(ind);

            cnt=1;

            //printf("calc ind %d cnt 1 ans%lld \n",ind,ans);

        }

        else if(maz[ind]=='['){

            ind++;

            p tmp=calc(ind);

            ans+=cnt*tmp.first;

            ind=tmp.second+1;

            cnt=1;

        }

    }

    //printf("calc start at %d end at %d ans = %lld\n",st,ind,ans);

    return p(ans,ind);

}



int main(){

    //freopen("input.txt","r",stdin);

    while(scanf("%s",maz)==1){

        long long a,b;

        scanf("%lld%lld",&a,&b);

        if(a==9){

            puts("A");

            continue;

        }

        else if(b==9){

            puts("B");

            continue;

        }

        long long ans=calc(0).first;

        if(ans==a){

            puts("B");

        }

        else puts("A");

    }

    return 0;

}