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

「爱情、让人受尽委屈。」 2022-06-13 07:50 155阅读 0赞

# 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

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;
    }