Codeforces 995 E

E - Number Clicker

思路：双向搜索

代码：

#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
//#define mp make_pair
#define pb push_back
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pii pair<int, int>
#define piii pair<int,pii>
#define mem(a, b) memset(a, b, sizeof(a))
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);
//head

int MOD;
int u, v, p;
map<int, pii>mp;
LL q_pow(LL n, LL k) {
    LL ans = 1;
    while(k) {
        if(k&1) ans = (ans * n) % MOD;
        n = (n*n) % MOD;
        k >>= 1;
    }
    return ans;
}
void print(int pos1, int pos2, int ty, int tt) {
    vector<int>vc;
    if(ty == 1) {
        int t = pos1;
        while(t != u) {
            if(mp[t].fi == 1) {
                vc.pb(1);
                t = (t + MOD - 1) % MOD;
            }
            else if(mp[t].fi == 2) {
                t = (t + 1) % MOD;
                vc.pb(2);
            }
            else if(mp[t].fi == 3) {
                 t = q_pow(t, MOD - 2) % MOD;
                vc.pb(3);
            }
        }
        reverse(vc.begin(), vc.end());
        vc.pb(tt);
        t = pos2;
        while(t != v) {
            if(mp[t].fi == 1) {
                vc.pb(2);
                t = (t + MOD - 1) % MOD;
            }
            else if(mp[t].fi == 2) {
                t = (t + 1) % MOD;
                vc.pb(1);
            }
            else if(mp[t].fi == 3) {
                 t = q_pow(t, MOD - 2) % MOD;
                vc.pb(3);
            }
        }
    }
    else {
        int t = pos2;
        while(t != u) {
            if(mp[t].fi == 1) {
                vc.pb(1);
                t = (t + MOD - 1) % MOD;
            }
            else if(mp[t].fi == 2) {
                t = (t + 1) % MOD;
                vc.pb(2);
            }
            else if(mp[t].fi == 3) {
                 t = q_pow(t, MOD - 2) % MOD;
                vc.pb(3);
            }
        }
        reverse(vc.begin(), vc.end());
        if(tt != 3)vc.pb(3-tt);
        else vc.pb(tt);
        t = pos1;
        while(t != v) {
            if(mp[t].fi == 1) {
                vc.pb(2);
                t = (t + MOD - 1) % MOD;
            }
            else if(mp[t].fi == 2) {
                t = (t + 1) % MOD;
                vc.pb(1);
            }
            else if(mp[t].fi == 3) {
                 t = q_pow(t, MOD - 2) % MOD;
                vc.pb(3);
            }
        }
    }
    //cout << pos1 << " " << pos2 << " " << ty << endl;
    printf("%d
", (int)vc.size());
    for (int i = 0; i < vc.size(); i++) printf("%d ", vc[i]);
}
int main() {
    scanf("%d %d %d", &u, &v, &p);
    MOD = p;
    queue<pii>q;
    if(u == v) return 0*puts("0");
    q.push({u, 1});
    q.push({v, 2});
    mp[u] = {u, 1};
    mp[v] = {v, 2};
    while(!q.empty()) {
        pii p = q.front();
        q.pop();
        int a = (p.fi + 1) % MOD;
        if(mp.find(a) != mp.end() && mp[a].se != p.se) {
            print(p.fi, a, p.se, 1);
            break;
        }
        else if(mp.find(a) == mp.end()){
            mp[a] = {1, p.se};
            q.push({a, p.se});
        }
        a = (p.fi + MOD - 1) % MOD;
        if(mp.find(a) != mp.end() && mp[a].se != p.se) {
            print(p.fi, a, p.se, 2);
            break;
        }
        else if(mp.find(a) == mp.end()){
            mp[a] = {2, p.se};
            q.push({a, p.se});
        }
        a = q_pow(p.fi, MOD - 2) % MOD;
        if(mp.find(a) != mp.end() && mp[a].se != p.se) {
            print(p.fi, a, p.se, 3);
            break;
        }
        else if(mp.find(a) == mp.end()){
            mp[a] = {3, p.se};
            q.push({a, p.se});
        }
    }
    return 0;
}