Submission #759272

#	Time	Username	Problem	Language	Result	Execution time	Memory
759272		fanwen	Tracks in the Snow (BOI13_tracks)	C++17	100 / 100	573 ms	138908 KiB

tracks

/**
 *      author : pham van sam 
 *      created : 16 June 2023 (Friday)
 **/

#include <bits/stdc++.h>

using namespace std;
using namespace chrono;

#define MASK(x) (1LL << (x))
#define BIT(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for (int i = 0, _n = n; i < _n; ++i)
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; --i)
#define FORE(it, s) for (__typeof(s.begin()) it = (s).begin(); it != (s).end(); ++it)

template <typename U, typename V> bool maximize(U &A, const V &B) { return (A < B) ? (A = B, true) : false; }
template <typename U, typename V> bool minimize(U &A, const V &B) { return (A > B) ? (A = B, true) : false; }

const int MAXN = 4e3 + 5;
const int dir[] = {1, -1, 0, 0, 0, 0, 1, -1};

int N, M, dp[MAXN][MAXN];
char a[MAXN][MAXN];

void process(void) {
    cin >> N >> M;
    FOR(i, 1, N) FOR(j, 1, M) cin >> a[i][j];
    deque <pair <int, int>> q;
    memset(dp, 0x3f, sizeof dp);
    q.emplace_front(1, 1); dp[1][1] = 1;
    while(!q.empty()) {
        auto [u, v] = q.front(); q.pop_front();
        REP(i, 4) {
            int x = u + dir[i];
            int y = v + dir[i + 4];
            if(x < 1 || x > N || y < 1 || y > M) continue;
            if(a[x][y] == '.') continue;
            int cost = (a[x][y] != a[u][v] ? 1 : 0);
            if(minimize(dp[x][y], dp[u][v] + cost)) {
                if(!cost) q.emplace_front(x, y);
                else q.emplace_back(x, y);
            }
        }
    }
    int ans = 0;
    FOR(i, 1, N) FOR(j, 1, M) if(a[i][j] != '.') {
        maximize(ans, dp[i][j]);
    }
    cout << ans;
}

signed main() {

    #define TASK "tracks"
    if(fopen(TASK".inp", "r")) {
        freopen(TASK".inp", "r", stdin);
        freopen(TASK".out", "w", stdout);
    }

    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    auto start_time = steady_clock::now();
    int test = 1;
    // cin >> test;
    for (int i = 1; i <= test; ++i) {
        process();
        // cout << '\n';
    }

    auto end_time = steady_clock::now();

    cerr << "\nExecution time : " << duration_cast<milliseconds> (end_time - start_time).count() << "[ms]" << endl;

    return (0 ^ 0);
}

Compilation message (stderr)

tracks.cpp: In function 'int main()':
tracks.cpp:59:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   59 |         freopen(TASK".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
tracks.cpp:60:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   60 |         freopen(TASK".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 30 / 30
• Subtask 2: 70 / 70