题目链接
1 #include <bits/stdc++.h>
2 # define LL long long
3 using namespace std;
4
5 bool dfs(vector<int> &num, vector<string> &res){
6 if(num.size()==1) {
7 if(num[0]==24) return true;
8 return false;
9 }
10
11 string tmp;
12 vector<int> nexted;
13 for(int i=0;i<num.size()-1;++i){
14
15 for(int j=i+1;j<num.size();++j){
16 int a=num[i];
17 int b=num[j];
18
19 if(a<b) swap(a,b);
20
21 nexted.clear();
22 for(int k=0;k<num.size();++k){
23 if(k==i || k==j) continue;
24 nexted.push_back(num[k]);
25 }
26 nexted.push_back(a+b);
27 tmp=to_string(a)+"+"+to_string(b)+"="+to_string(a+b);
28 res.push_back(tmp);
29 if(dfs(nexted,res)) return true;
30 res.pop_back();
31
32 nexted.clear();
33 for(int k=0;k<num.size();++k){
34 if(k==i || k==j) continue;
35 nexted.push_back(num[k]);
36 }
37 nexted.push_back(a-b);
38
39 tmp=to_string(a)+"-"+to_string(b)+"="+to_string(a-b);
40 res.push_back(tmp);
41 if(dfs(nexted,res)) return true;
42 res.pop_back();
43
44 nexted.clear();
45 vector<int> tmpv;
46 for(int k=0;k<num.size();++k){
47 if(k==i || k==j) continue;
48 nexted.push_back(num[k]);
49 }
50 nexted.push_back(a*b);
51 tmp=to_string(a)+"*"+to_string(b)+"="+to_string(a*b);
52 res.push_back(tmp);
53 if(dfs(nexted,res)) return true;
54 res.pop_back();
55
56 if(b!=0 && a%b==0){
57 nexted.clear();
58 for(int k=0;k<num.size();++k){
59 if(k==i || k==j) continue;
60 nexted.push_back(num[k]);
61 }
62 nexted.push_back(a/b);
63 tmp=to_string(a)+"/"+to_string(b)+"="+to_string(a/b);
64 res.push_back(tmp);
65 if(dfs(nexted,res)) return true;
66 res.pop_back();
67 }
68 }
69 }
70 return false;
71 }
72
73 int main(){
74 vector<int> num(4,0);
75 for(int i=0;i<4;++i){
76 int t;
77 scanf("%d", &t);
78 num[i]=t;
79 }
80 vector<string> res;
81 bool r=dfs(num,res);
82 if(!r){
83 printf("No answer!\n");
84 return 0;
85 }
86 for(auto &s:res){
87 cout<<s<<"\n";
88 }
89 return 0;
90 }
