hdu2266——How Many Equations Can You Find

Problem Description

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.

 

Input

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.

 

Output

The output contains one line for each data set : the number of ways you can find to make the equation.

 

Sample Input

123456789 321 1

 

Sample Output

181

 

题目大意：给你一个字符串，要你在字符之间加+、-、或者不加，使得最后的结果为n。问你总共有多少种？

解题思路：dfs，对每一个位置进行判断，尝试着放入每一个符号，查看最后的结果，是否为n.

代码：

#include <iostream>#include <cstdio>#include <cstring>using namespace std;typedef long long ll;char str[15];ll n,cnt;int len;void dfs(int k,int sum){    if(k==len)    {        if(sum==n)            cnt++;        return;    }    ll temp=0;    for(int i=k;i<len;i++)    {        temp=temp*10+(str[i]-'0');        dfs(i+1,sum+temp);        if(k)            dfs(i+1,sum-temp);    }}int main(){    while(~scanf("%s%lld",str,&n))    {        len=strlen(str);        cnt=0;        dfs(0,0);        printf("%lld\n",cnt);    }    return 0;}