ABC Gene http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=2708

aoj2708.cpp

#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(a)-1;i>=b;i--)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define printV(v) for(auto x : v){cout << x << " ";} cout << endl
#define printVS(vs) for(auto x : vs){cout << x << endl;}
#define printVV(vv) for(auto v : vv){for(auto&& x : v){cout << x << " ";}cout << endl;}
#define printP(p) cout << p.first << " " << p.second << endl
#define printVP(vp) for(auto p : vp) printP(p);

typedef long long ll;
typedef pair<int, int> Pii;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<Pii> vp;
typedef vector<vector<int>> Graph;
const int inf = 1e9;
const int mod = 1e9 + 7;

bool dfs(string s) {
    if (s == "ABC") {
        return true;
    } else if (s.find("ABC") == string::npos) {
        return false;
    }

    vector<bool> valid(3, true);
    {
        string t;
        int i = 0;
        while (i < s.size()) {
            if (i <= (int)s.size() - 3 && s.substr(i, 3) == "ABC") {
                i += 3;
            } else {
                t += s[i];
                i++;
            }
        }
        rep(i, t.size()) {
            valid[t[i] - 'A'] = false;
        }
    }

    bool ret = false;
    rep(k, 3) {
        if (!valid[k]) continue;
        string t;
        int i = 0;
        while (i < s.size()) {
            if (i <= (int)s.size() - 3 && s.substr(i, 3) == "ABC") {
                t += 'A' + k;
                i += 3;
            } else {
                t += s[i];
                i++;
            }
        }
        ret |= dfs(t);
    }
    return ret;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    string s;
    cin >> s;
    cout << (dfs(s) ? "Yes" : "No") << endl;
}