UVA 10344

题目大意：输入五个数， 判断是否存在情况使得式子( ( a(1) o a(2) ) o a(3) ) o a(4) ) o4 a(5)等于23。五个数的任意排序，o为运算符‘+’，‘-’，或‘*’。

解题思路：运算符的顺序用三进制来表示，五个数的全排序用next_permutation来计算。

ac代码：

#include <iostream>#include <cmath>#include <algorithm>using namespace std;int a[10], re[4], sum, flag;int compute(){int sum = a[0];for (int i=0; i<4; i++){if (re[i] == 0)sum += a[i+1];else if (re[i] == 1)sum -= a[i+1];elsesum *= a[i+1];}return sum;}int main(){while (scanf("%d", &a[0])!=EOF){flag = 0;for (int i=1; i<5; i++)scanf("%d", &a[i]);if (!a[0] && !a[1] && !a[2] && !a[3] && !a[4])break;for (int i=0; i<pow(3, 4); i++){sort(a, a+5);for (int j=0,cnt=1; j<4; j++,cnt*=3)re[j] = i / cnt % 3;do{if (compute() == 23)flag = 1;}while (next_permutation(a, a+5));}if (flag)printf("Possible\n");elseprintf("Impossible\n");}return 0;}