首页 > ACM题库 > HDU-杭电 > hdu 2266 How Many Equations Can You Find-DFS-[解题报告]C++
2014
01-04

hdu 2266 How Many Equations Can You Find-DFS-[解题报告]C++

How Many Equations Can You Find

问题描述 :

Now give you an string which only contains 0, 1 ,2 ,3 ,4 ,5 ,6 ,7 ,8 ,9.You are asked to add the sign ‘+’ or ’-’ between the characters. Just like give you a string “12345”, you can work out a string “123+4-5”. Now give you an integer N, please tell me how many ways can you find to make the result of the string equal to N .You can only choose at most one sign between two adjacent characters.

输入:

Each case contains a string s and a number N . You may be sure the length of the string will not exceed 12 and the absolute value of N will not exceed 999999999999.

输出:

Each case contains a string s and a number N . You may be sure the length of the string will not exceed 12 and the absolute value of N will not exceed 999999999999.

样例输入:

123456789 3
21 1

样例输出:

18
1

#include<iostream>
 #include<cstring>
 #include<cstdio>
 using namespace std;
 __int64 num,n,len;
 char str[15];
 void DFS(__int64 x,__int64 sum)
 {
     if(x==len)
     {
         if(sum==n)
         
             num++;
             return ;
         
     }
     __int64 k=0;//核心的东东  短短的几句  却是指数级的搜索量啊
     for(int i=x;i<len;i++)//这里刚开始写成了从0开始,哎合适能搜到头啊
     {
         k=k*10+str[i]-'0';
         DFS(i+1,sum+k);
         if(x!=0)//第一个数字前不能加“-”号
             DFS(i+1,sum-k);
     }
 }
 
 
 int main()
 {
     while(scanf("%s %I64d",str,&n)!=EOF)
     {
         len=strlen(str);
         num=0;
         DFS(0,0);
         printf("%I64d\n",num);
     }
     return 0;
 }

解题转自:http://www.cnblogs.com/heat-man/archive/2013/04/23/3037935.html


,