Codeforces 1291A - Even But Not Even

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 void solve(){
 4     int n,i,n1=0;
 5     string s;
 6     cin>>n>>s;
 7     for(i=0;i<n;i++)
 8         if((s[i]-‘0‘)%2)
 9             n1++;
10     if(n1&&n1%2==0){
11         while(n&&(s[n-1]-‘0‘)%2==0){
12             s.erase(n-1,1);
13             n--;
14         }
15     }
16     else if(n1>2){
17         while(n&&(s[n-1]-‘0‘)%2==0){
18             s.erase(n-1,1);
19             n--;
20         }
21         s.erase(n-1,1);//遇到奇数，删除后继续删偶数
22         n--;
23         while(n&&(s[n-1]-‘0‘)%2==0){
24             s.erase(n-1,1);
25             n--;
26         }
27     }
28     else
29         s="-1";
30     cout<<s<<‘\n‘;
31 }
32 int main(){
33     ios::sync_with_stdio(0);
34     cin.tie(0);cout.tie(0);
35     int T;cin>>T;while(T--)
36         solve();
37     
38     return 0;
39 }