题解 | 玛雅人的密码

//KY11 玛雅人的密码
#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
#include <unordered_map>
using namespace std;
int n;
string s;
unordered_map<string,int>mp;
int main()
{
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin>>n;
    cin>>s;
    if(n<4) {cout<<-1<<'\n';return 0;}
    queue<string>q;
    q.push(s);
    mp[s]=0;
    bool flag=false;
    while(q.size())
    {
        string now=q.front();
        q.pop();
        if(now.find("2012")!=string::npos){
            flag=true;
            cout<<mp[now]<<"\n";
            break;
        }
        for(int i=0;i<now.length()-1;i++){
            string s1=now;
            char op=s1[i];
            s1[i]=s1[i+1];
            s1[i+1]=op;
            if(mp.count(s1)==0){
                q.push(s1);
                mp[s1]=mp[now]+1;
            }
        }
    }
    if(!flag) cout<<-1<<"\n";
    return 0;
}