HDU 2266 How Many Equations Can You Find （技巧性dfs）

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

解题思路：

代码很短，可以自己体会，注意的是第一个数字不能减。。一开始连思路都没。。感觉怎么做都要爆数据。。我还是太弱了，看了博客后恍然大悟。。记下来记下来

代码：

#include<algorithm>#include<iostream>#include<cstring>#include<cstdio>#include<math.h>#include<string>#include<stdio.h>#include<queue>#include<stack>using namespace std;char s[20];long long tot,n;void dfs(int sum,int p){    if(p==strlen(s))    {        if(sum==n)            tot++;        return;    }    int i,k=0;    for(i=p;i<strlen(s);i++)    {        k=k*10+s[i]-'0';        dfs(sum+k,i+1);        if(p!=0)            dfs(sum-k,i+1);    }}int main(){    while(scanf("%s%lld",s,&n)!=EOF)    {        tot=0;        dfs(0,0);        printf("%lld\n",tot);    }    return 0;}