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 3
21 1
Sample Output
18
1
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;
}