Submission #985087

#	Time	Username	Problem	Language	Result	Execution time	Memory
985087		MegatronRobo	Mecho (IOI09_mecho)	C++17	84 / 100	198 ms	12032 KiB

mecho

#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using db = long double; // or double, if TL is tight
using str = string; // yay python!

using pi = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;

using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vpi = vector<pi>;
using vpl = vector<pl>;
using vpd = vector<pd>;


#define tcT template<class T
#define tcTU tcT, class U

// ^ lol this makes everything look weird but I'll try it
tcT> using V = vector<T>;
tcT, size_t SZ> using AR = array<T,SZ>;
tcT> using PR = pair<T,T>;

// pairs
#define mp make_pair
#define f first
#define s second

// vectors
// oops size(x), rbegin(x), rend(x) need C++17
#define sz(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) x.rbegin(), x.rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front
#define rtn return

#define lb lower_bound
#define ub upper_bound
tcT> int lwb(V<T>& a, const T& b) { return int(lb(all(a),b)-bg(a)); }

// loops
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define rep(a) F0R(_,a)
#define each(a,x) for (auto& a: x)

const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5;
const ll INF = 1e18; // not too close to LLONG_MAX
const db PI = acos((db)-1);
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
template<class T> using pqg = priority_queue<T,vector<T>,greater<T>>;

// bitwise ops
// also see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
constexpr int pct(int x) { return __builtin_popcount(x); } // # of bits set
constexpr int bits(int x) { // assert(x >= 0); // make C++11 compatible until USACO updates ...
	return x == 0 ? 0 : 31-__builtin_clz(x); } // floor(log2(x))

constexpr int p2(int x) { return 1<<x; }
constexpr int msk2(int x) { return p2(x)-1; }

ll cdiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll fdiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down

tcT> bool ckmin(T& a, const T& b) {
	return b < a ? a = b, 1 : 0; } // set a = min(a,b)

tcT> bool ckmax(T& a, const T& b) {
	return a < b ? a = b, 1 : 0; }

tcTU> T fstTrue(T lo, T hi, U f) {
	hi ++; assert(lo <= hi); // assuming f is increasing
	while (lo < hi) { // find first index such that f is true
		T mid = lo+(hi-lo)/2;
		f(mid) ? hi = mid : lo = mid+1;
	}
	return lo;
}

tcTU> T lstTrue(T lo, T hi, U f) {
	lo --; assert(lo <= hi); // assuming f is decreasing
	while (lo < hi) { // find first index such that f is true
		T mid = lo+(hi-lo+1)/2;
		f(mid) ? lo = mid : hi = mid-1;
	}
	return lo;
}

tcT> void remDup(vector<T>& v) { // sort and remove duplicates
	sort(all(v)); v.erase(unique(all(v)),end(v)); }

tcTU> void erase(T& t, const U& u) { // don't erase
	auto it = t.find(u); assert(it != end(t));
	t.erase(it); } // element that doesn't exist from (multi)set

#define tcTUU tcT, class ...U

inline namespace Helpers {
	//////////// is_iterable
	// https://stackoverflow.com/questions/13830158/check-if-a-variable-type-is-iterable
	// this gets used only when we can call begin() and end() on that type
	tcT, class = void> struct is_iterable : false_type {};
	tcT> struct is_iterable<T, void_t<decltype(begin(declval<T>())),
	                                  decltype(end(declval<T>()))
	                                 >
	                       > : true_type {};
	tcT> constexpr bool is_iterable_v = is_iterable<T>::value;

	//////////// is_readable
	tcT, class = void> struct is_readable : false_type {};
	tcT> struct is_readable<T,
	        typename std::enable_if_t<
	            is_same_v<decltype(cin >> declval<T&>()), istream&>
	        >
	    > : true_type {};
	tcT> constexpr bool is_readable_v = is_readable<T>::value;

	//////////// is_printable
	// // https://nafe.es/posts/2020-02-29-is-printable/
	tcT, class = void> struct is_printable : false_type {};
	tcT> struct is_printable<T,
	        typename std::enable_if_t<
	            is_same_v<decltype(cout << declval<T>()), ostream&>
	        >
	    > : true_type {};
	tcT> constexpr bool is_printable_v = is_printable<T>::value;
}


inline namespace Input {
	tcT> constexpr bool needs_input_v = !is_readable_v<T> && is_iterable_v<T>;
	tcTUU> void re(T& t, U&... u);
	tcTU> void re(pair<T,U>& p); // pairs

	// re: read
	tcT> typename enable_if<is_readable_v<T>,void>::type re(T& x) { cin >> x; } // default
	tcT> void re(complex<T>& c) { T a,b; re(a,b); c = {a,b}; } // complex
	tcT> typename enable_if<needs_input_v<T>,void>::type re(T& i); // ex. vectors, arrays
	tcTU> void re(pair<T,U>& p) { re(p.f,p.s); }
	tcT> typename enable_if<needs_input_v<T>,void>::type re(T& i) {
		each(x,i) re(x); }

	tcTUU> void re(T& t, U&... u) { re(t); re(u...); } // read multiple

	// rv: resize and read vectors
	void rv(size_t) {}
	tcTUU> void rv(size_t N, V<T>& t, U&... u);

	template<class...U> void rv(size_t, size_t N2, U&... u);
	tcTUU> void rv(size_t N, V<T>& t, U&... u) {
		t.rsz(N); re(t);
		rv(N,u...); }

	template<class...U> void rv(size_t, size_t N2, U&... u) {
		rv(N2,u...); }

	// dumb shortcuts to read in ints
	void decrement() {} // subtract one from each
	tcTUU> void decrement(T& t, U&... u) { --t; decrement(u...); }
	#define ints(...) int __VA_ARGS__; re(__VA_ARGS__);
	#define int1(...) ints(__VA_ARGS__); decrement(__VA_ARGS__);
}


inline namespace ToString {
	tcT> constexpr bool needs_output_v = !is_printable_v<T> && is_iterable_v<T>;

	// ts: string representation to print
	tcT> typename enable_if<is_printable_v<T>,str>::type ts(T v) {
		stringstream ss; ss << fixed << setprecision(15) << v;
		return ss.str(); } // default

	tcT> str bit_vec(T t) { // bit vector to string
		str res = "{"; F0R(i,sz(t)) res += ts(t[i]);
		res += "}"; return res; }
	str ts(V<bool> v) { return bit_vec(v); }
	template<size_t SZ> str ts(bitset<SZ> b) { return bit_vec(b); } // bit vector
	tcTU> str ts(pair<T,U> p); // pairs
	tcT> typename enable_if<needs_output_v<T>,str>::type ts(T v); // vectors, arrays
	tcTU> str ts(pair<T,U> p) { return "("+ts(p.f)+", "+ts(p.s)+")"; }
	tcT> typename enable_if<is_iterable_v<T>,str>::type ts_sep(T v, str sep) {
		// convert container to string w/ separator sep
		bool fst = 1; str res = "";
		for (const auto& x: v) {
			if (!fst) res += sep;
			fst = 0; res += ts(x);
		}
		return res;
	}
	tcT> typename enable_if<needs_output_v<T>,str>::type ts(T v) {
		return "{"+ts_sep(v,", ")+"}"; }

	// for nested DS
	template<int, class T> typename enable_if<!needs_output_v<T>,vs>::type
	  ts_lev(const T& v) { return {ts(v)}; }
	template<int lev, class T> typename enable_if<needs_output_v<T>,vs>::type
	  ts_lev(const T& v) {
		if (lev == 0 || !sz(v)) return {ts(v)};
		vs res;
		for (const auto& t: v) {
			if (sz(res)) res.bk += ",";
			vs tmp = ts_lev<lev-1>(t);
			res.ins(end(res),all(tmp));
		}
		F0R(i,sz(res)) {
			str bef = " "; if (i == 0) bef = "{";
			res[i] = bef+res[i];
		}
		res.bk += "}";
		return res;
	}
}


inline namespace Output {
	template<class T> void pr_sep(ostream& os, str, const T& t) { os << ts(t); }
	template<class T, class... U> void pr_sep(ostream& os, str sep, const T& t, const U&... u) {
		pr_sep(os,sep,t); os << sep; pr_sep(os,sep,u...); }
	// print w/ no spaces
	template<class ...T> void pr(const T&... t) { pr_sep(cout,"",t...); }

	// print w/ spaces, end with newline
	void ps() { cout << "\n"; }
	template<class ...T> void ps(const T&... t) { pr_sep(cout," ",t...); ps(); }

	// debug to cerr
	template<class ...T> void dbg_out(const T&... t) {
		pr_sep(cerr," | ",t...); cerr << endl; }
	void loc_info(int line, str names) {
		cerr << "Line(" << line << ") -> [" << names << "]: "; }
	template<int lev, class T> void dbgl_out(const T& t) {
		cerr << "\n\n" << ts_sep(ts_lev<lev>(t),"\n") << "\n" << endl; }
	#ifdef LOCAL
		#define dbg(...) loc_info(__LINE__,#__VA_ARGS__), dbg_out(__VA_ARGS__)
		#define dbgl(lev,x) loc_info(__LINE__,#x), dbgl_out<lev>(x)
	#else // don't actually submit with this
		#define dbg(...) 0
		#define dbgl(lev,x) 0
	#endif
}

inline namespace FileIO {
	void setIn(str s)  { freopen(s.c_str(), "r", stdin); }
	void setOut(str s) { freopen(s.c_str(), "w", stdout); }
	void setIO(str s = "") {
		cin.tie(0)->sync_with_stdio(0); // unsync C / C++ I/O streams
		// cin.exceptions(cin.failbit);
		// throws exception when do smth illegal
		// ex. try to read letter into int
		if (sz(s)) setIn(s+".in"), setOut(s+".out"); // for old USACO
	}
}
/*
Binary search on ans
The more the bear waits, more chances of it getting caught, last_true, hi = the time bees took to reach bear's home adjacent cells

1) First we start BFS from bee hives and then determine the time taken to every grid
2) then we do binary search on ans, and assign dist/time to every node as mid+time_now_from_start/S and we will push into queue only when if it is strictly less than bees time taken

*/
int r_change[] = {0, 0, 1, -1};
int c_change[] = {1, -1, 0, 0};
int main(){
    int n, sp;
    cin>>n>>sp;

    V<string> grid(n);
    V<pi> hives;
    pi mecho, home;
    FOR(i, 0, n){
        string s;
        cin>>s;
        FOR(j, 0, n){
            if(s[j]=='M'){
                mecho={i, j};
            }else if(s[j]=='D'){
                home = {i, j};
            }else if(s[j]=='H'){
                hives.pb({i, j});
            }
        }
        grid[i]=s;
    }

    // starting BFS from hives to determing the dist to every grid

    V<vpi> dist(n, vpi(n, {INT_MAX, INT_MAX})); // first for bear and second for bee hives
    queue<pi> q;
    each(t, hives){
        q.push(t);
        dist[t.f][t.s].s = 0;
    }
    while(!q.empty()){
        const auto [r, c] = q.ft;
        q.pop();

        FOR(i, 0, 4){
            int new_r = r+r_change[i];
            int new_c = c+c_change[i];

            if(new_r < 0 || new_r >= n || new_c < 0 || new_c >= n || dist[new_r][new_c].s != INT_MAX || grid[new_r][new_c]=='T')
                continue;
            q.push({new_r, new_c});
            dist[new_r][new_c].s = dist[r][c].s+1;
        }
    }
    dist[home.f][home.s].s = INT_MAX;

    // determining max time it took for bees to reach home adjacent cells
    int time_took_max = 0;
    FOR(i, 0, 4){
        if(home.f+r_change[i] < 0 || home.f+r_change[i] >= n || home.s+c_change[i] < 0 || home.s+c_change[i] >= n || dist[home.f+r_change[i]][home.s+c_change[i]].s == INT_MAX)
            continue;
        time_took_max = max(time_took_max, dist[home.f+r_change[i]][home.s+c_change[i]].s);
    }

    // last_true
    int lo=-1, hi=time_took_max;
    while(lo<hi){
        int mid=lo+(hi-lo+1)/2;
        // to check if bear is able to escape if it waits this much time
        FOR(i, 0, n){
            FOR(j, 0, n){
                dist[i][j].f = INT_MAX;
            }
        }
        dist[mecho.f][mecho.s].f = 0;
        V<V<double>> pup(n, V<double>(n, INT_MAX));
        pup[mecho.f][mecho.s] = mid;

        q.push(mecho);
        while(!q.empty()){
            const auto [r, c] = q.ft;
            q.pop();

            FOR(i, 0, 4){
                int new_r = r+r_change[i];
                int new_c = c+c_change[i];

                if(new_r < 0 || new_r >= n || new_c < 0 || new_c >= n || dist[new_r][new_c].f != INT_MAX || grid[new_r][new_c]=='T' || (float)mid+(float)(dist[r][c].f+1)/(float)sp>=dist[new_r][new_c].s){
                    continue;
                }
                q.push({new_r, new_c});
                pup[new_r][new_c] = (float)mid+(float)(dist[r][c].f+1)/(float)sp;
                dist[new_r][new_c].f = dist[r][c].f+1;  
            }         
        }
        // cout<<endl;
        // cout<<"mid: "<<mid<<endl;
        // FOR(i, 0, n){
        //     FOR(j, 0, n){
        //         if(pup[i][j]==INT_MAX)
        //             cout<<-1<<" ";
        //         else{
        //             cout<<setprecision(2);
        //             cout<<pup[i][j]<<" ";
        //         }
        //     }
        //     cout<<endl;
        // }
        // cout<<endl;
        // FOR(i, 0, n){
        //     FOR(j, 0, n){   
        //         if(dist[i][j].f==INT_MAX)
        //             cout<<-1<<" ";
        //         else
        //             cout<<dist[i][j].f<<" ";
        //     }
        //     cout<<endl;
        // }
        // cout<<endl;
        // FOR(i, 0, n){
        //     FOR(j, 0, n){   
        //         if(dist[i][j].s==INT_MAX)
        //             cout<<-1<<" ";
        //         else
        //             cout<<dist[i][j].s<<" ";
        //     }
        //     cout<<endl;
        // }
        bool possible = false;
        FOR(i, 0, 4){
            int new_r=home.f+r_change[i], new_c=home.s+c_change[i];
            if(new_r < 0 || new_r >= n || new_c < 0 || new_c >= n || pup[new_r][new_c] == INT_MAX)
                continue;
            possible = true;
            break;
        }
        if(possible){
            // possible to reach
            lo=mid;
        }else{
            hi=mid-1;
        }
    }
    cout<<lo<<endl;
}

Compilation message (stderr)

mecho.cpp: In function 'void FileIO::setIn(str)':
mecho.cpp:261:30: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  261 |  void setIn(str s)  { freopen(s.c_str(), "r", stdin); }
      |                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
mecho.cpp: In function 'void FileIO::setOut(str)':
mecho.cpp:262:30: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  262 |  void setOut(str s) { freopen(s.c_str(), "w", stdout); }
      |                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 84 / 100