Power Calculus UVA

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查看网上别人打表的做法，运算最多为13次，所以我们最多循环13次。每次循环的时候设置当前的最大深度，然后在每次的dfs中首先查看是否能够继续向下循环，然后再判断按照当前的状况是否有可能得到最终的解。再将上次新产生的值和当前的旧值进行加法以及减法组合产生新的值，进行下一步的递归，查看是否能够得到最终的解即可。具体实现见如下代码：

#include<iostream>#include<vector>#include<string>#include<set>#include<stack>#include<queue>#include<map>#include<algorithm>#include<cmath>#include<iomanip>#include<cstring>#include<sstream>#include<cstdio>#include<deque>using namespace std;int n;int arr[100];int depth;bool Solve(int length_a,int cur_d,int cur_da){if (cur_d == depth){if (cur_da == n) return true;return false;}int record = 0;for (int i = 0; i < length_a; i++) record = max(record,arr[i]);if (record*(1 << (depth - cur_d)) < n) return false;for (int i = 0; i < length_a; i++){arr[length_a] = cur_da + arr[i];if (Solve(length_a + 1, cur_d + 1, arr[length_a])) return true;arr[length_a] = abs(cur_da-arr[i]);if (Solve(length_a + 1, cur_d + 1, arr[length_a])) return true;}return false;}int main(){while (cin >> n&&n){for (depth = 0; depth < 13; depth++){arr[0] = 1;if (Solve(1, 0, 1))break;}cout << depth << endl;}return 0;}

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