按字典序输出所有在123..n之间插入'+','-',' '结果为0的表达式。.
http://train.usaco.org/usacoprob2?a=jUh88pMwCSQ&S=zerosum
/*
TASK:zerosum
LANG:C++
*/
#include<cstdio>
#include<string>
#include<algorithm>
using namespace std;
#define N 15
int n;
int k[N],cnt,s[3]={0,1,-1};
string ans[7000];
void dfs(int d){
if(d>n){
int sum=0,c=1;
for(int i=2;i<=n;i++){
if(k[i]){
sum+=c;
c=i*k[i];
}else{
c=c*10+(c>0?i:-i);
}
}
sum+=c;
if(sum==0){
ans[++cnt]+="1";
for(int i=2;i<=n;i++){
ans[cnt]+=k[i]>0?'+':k[i]<0?'-':' ';
ans[cnt]+=i+'0';
}
}
return;
}
for(int i=0;i<=2;i++){
k[d]=s[i];
dfs(d+1);
}
}
int main(){
freopen("zerosum.in","r",stdin);
freopen("zerosum.out","w",stdout);
scanf("%d",&n);
dfs(2);
for(int i=1;i<=cnt;i++){
printf("%s\n",ans[i].c_str());
}
}