搜索,最后判断一下是否结果为0就行。
#include <iostream> #include <cstdio> #include <cmath> #include <algorithm> #include <vector> #include <iomanip> #include <cstring> #include <map> #include <queue> #include <set> #include <cassert> #include <stack> #include <bitset> #define mkp make_pair using namespace std; const double EPS=1e-8; typedef long long lon; const lon SZ=200030,INF=0x7FFFFFFF,mod=9901; char arr[]={'+','-',' '}; vector<string> res; int cal(string str) { int pos=0; pos=str.find_first_of("+-",pos); if(pos==-1)return 123456789; int ope1=0,ope2=0; for(int i=0;i<pos;++i) { if(str[i]!=' ') { ope1=ope1*10+str[i]-'0'; } } int oldpos=++pos; for(;;) { pos=str.find_first_of("+-",oldpos); if(pos==-1)pos=str.size(); for(int i=oldpos;i<pos;++i) { if(str[i]!=' ') { ope2=ope2*10+str[i]-'0'; } } if(str[oldpos-1]=='+')ope1=ope1+ope2,ope2=0; else ope1=ope1-ope2,ope2=0; oldpos=pos+1; if(pos==str.size())break; } return ope1; } void dfs(int pos,int n,string &str) { if(pos==n+1) { if(cal(str)==0) { res.push_back(str); } return; } for(int i=0;i<3;++i) { str+=arr[i]; str+=pos+'0'; dfs(pos+1,n,str); str.erase(str.end()-2,str.end()); } } int main() { std::ios::sync_with_stdio(0); //freopen("d:\\1.txt","r",stdin); lon casenum; //cin>>casenum; //for(lon time=1;time<=casenum;++time) { int n; cin>>n; string str="1"; dfs(2,n,str); sort(res.begin(),res.end()); for(int i=0;i<res.size();++i) { cout<<res[i]<<endl; } } return 0; }