How Many Equations Can You Find
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1723 Accepted Submission(s): 1148
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
Author
dandelion
Source
HDU 8th Programming Contest Online
問題鏈接：HDU2266 How Many Equations Can You Find
問題簡述：給定一個只包含0-9數字的字符串，在字符之間添加“+”或“-”符號。例如字符串“12345”，可以有一個字符串“123+4-5”。同時，給定一個整數N，計算有多少種方法使加上“+”或“-”符號字符串後結果等於N。
問題分析：用DFS實現，窮盡搜索。
程序說明：（略）
參考鏈接：（略）
題記：（略）
AC的C++語言程序如下：
/* HDU2266 How Many Equations Can You Find */
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
string s;
LL n, ans;
void dfs(int k, LL num)
{
if(s[k] == '\0') {
if(num == n) ans++;
} else {
LL tmp = 0;
for(int i = k; s[i]; i++) {
tmp = tmp * 10 + s[i] - '0';
dfs(i + 1, num + tmp);
if(k) dfs(i + 1, num - tmp); // 首個數前不可帶符號
}
}
}
int main()
{
while(cin >> s >> n) {
ans = 0;
dfs(0, 0);
cout << ans << endl;
}
return 0;
}