51nod 1832 先序遍历与后序遍历（dfs+高精度）

http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1832

题意：

思路：

官方题解如下：

可以看一下这篇文章：https://wenku.baidu.com/view/a2a45aa0284ac850ad024261.html

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<queue>
 using namespace std;
 const int maxn = +;
 const int inf = 0x3f3f3f3f;
 
 int n;
 int a[maxn],b[maxn];
 
 struct BigInt
 {
     const static int mod = ;
     const static int DLEN = ;
     int a[],len;
     BigInt()
     {
         memset(a,,sizeof(a));
         len = ;
     }
     BigInt(int v)
     {
         memset(a,,sizeof(a));
         len = ;
         do
         {
             a[len++] = v%mod;
             v /= mod;
         }while(v);
     }
     BigInt(const char s[])
     {
         memset(a,,sizeof(a));
         int L = strlen(s);
         len = L/DLEN;
         if(L%DLEN)len++;
         int index = ;
         for(int i = L-;i >= ;i -= DLEN)
         {
             int t = ;
             int k = i - DLEN + ;
             if(k < )k = ;
             for(int j = k;j <= i;j++)
                 t = t* + s[j] - '';
             a[index++] = t;
         }
     }
     BigInt operator +(const BigInt &b)const
     {
         BigInt res;
         res.len = max(len,b.len);
         for(int i = ;i <= res.len;i++)
             res.a[i] = ;
         for(int i = ;i < res.len;i++)
         {
             res.a[i] += ((i < len)?a[i]:)+((i < b.len)?b.a[i]:);
             res.a[i+] += res.a[i]/mod;
             res.a[i] %= mod;
         }
         if(res.a[res.len] > )res.len++;
         return res;
     }
     BigInt operator *(const BigInt &b)const
     {
         BigInt res;
         for(int i = ; i < len;i++)
         {
             int up = ;
             for(int j = ;j < b.len;j++)
             {
                 int temp = a[i]*b.a[j] + res.a[i+j] + up;
                 res.a[i+j] = temp%mod;
                 up = temp/mod;
             }
             if(up != )
                 res.a[i + b.len] = up;
         }
         res.len = len + b.len;
         while(res.a[res.len - ] ==  &&res.len > )res.len--;
         return res;
     }
     void output()
     {
         printf("%d",a[len-]);
         for(int i = len-;i >= ;i--)
             printf("%04d",a[i]);
         printf("\n");
     }
 };
 BigInt ans;
 
 void dfs(int al, int ar, int bl, int br)
 {
     if(ar-al<=)  return;
     al++;
     br--;
     int cnt = ;
     int index = bl;
     while(a[al]!=b[index])  index++;
     int newar = al+index-bl+;
     int newbl = index+;
     cnt++;
     dfs(al,newar-,bl,index);
     if(ar-al!=index-bl)
     {
         cnt++;
         dfs(newar,ar,newbl,br);
     }
     if(cnt==)  ans=ans*;
 }
 
 int main()
 {
     //freopen("in.txt","r",stdin);
     ans = ;
     scanf("%d",&n);
     for(int i=;i<n;i++)  scanf("%d",&a[i]);
     for(int i=;i<n;i++)  scanf("%d",&b[i]);
     dfs(,n-,,n-);
     ans.output();
     return ;
 }