According to Bartjens UVA

很明显的暴力枚举，枚举的过程中会遇到关于表达式计算的问题，在暴力枚举中算是一个常见的问题吧

代码参考别人的，看了之后感觉在表达式计算的方面还有可以改进的地方

关于改进的问题等表示式计算模板出来再去考虑吧

#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iomanip>
#include<assert.h>
#include<vector>
#include<list>
#include<map>
#include<set>
#include<sstream>
#include<stack>
#include<queue>
#include<string>
#include<algorithm>
#pragma warning(disable:4996)
#define me(s)  memset(s,0,sizeof(s))
#define _for(i,a,b) for(int i=(a);i<(b);++i)
#define _rep(i,a,b) for(int i=(a);i<=(b);++i)
using namespace std;
typedef pair <int, int> pii;
typedef long long ll;
typedef unsigned long long llu;
const int MOD = 1e9 + 7;
const double pi = acos(-1.0);
const double eps = 1e-15;
int c[3] = { '*','+','-' };
const int maxn = 25;
char str[maxn], re[maxn];
int res[maxn], n, flag;
set<string> ouput;
void init()
{ouput.clear();n = strlen(str) - 1;flag = 1;
}
int cal()
{int num[maxn], num1[maxn], ans = 0, numn = 0, i, numn1 = 0, res1[maxn], resn = 0, res2[maxn], res2n = 0;num[0] = str[0] - '0';for (i = 0; i < n - 1; i++) {if (res[i] == 3) {if (num[numn] == 0) return 0;num[numn] = num[numn] * 10 + str[i + 1] - '0';}else {res1[resn++] = res[i];num[++numn] = str[i + 1] - '0';}}num1[0] = num[0];for (i = 0; i < resn; i++) {if (res1[i] == 0) {num1[numn1] *= num[i + 1];}else {res2[res2n++] = res1[i];num1[++numn1] = num[i + 1];}}ans = num1[0];for (i = 0; i < res2n; i++)if (res2[i] == 1) ans += num1[i + 1];else ans -= num1[i + 1];return ans;
}
void dfs(int cur)
{if (cur == n - 1) {int num = cal();if (num == 2000) {flag = 0;me(re);int k = 1;re[0] = str[0];for (int j = 0; j < cur; j++) {if (res[j] == 3) re[k++] = str[j + 1];else {re[k++] = c[res[j]];re[k++] = str[j + 1];}}ouput.insert(re);}return;}for (int i = 0; i < 4; i++) {res[cur] = i;dfs(cur + 1);}
}
void solve()
{if (strcmp(str, "2000=") == 0) {printf("  IMPOSSIBLE\n");return;}dfs(0);if(flag) printf("  IMPOSSIBLE\n");else {for (auto it : ouput)cout << "  " << it << '=' << endl;}
}
int main()
{int kcase = 0;while (scanf("%s", str) == 1 && str[0] != '='){init();printf("Problem %d\n", ++kcase);solve();}
}