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;
}