CSES - BOI 2026 Mirror Day 1

Submission details
Task:	Island
Sender:	Sebastian
Submission time:	2026-04-16 18:30:36 +0300
Language:	C++ (C++20)
Status:	READY
Result:	100

Feedback
subtask	verdict	score
#1	ACCEPTED	10
#2	ACCEPTED	6
#3	ACCEPTED	16
#4	ACCEPTED	28
#5	ACCEPTED	40

Test results
test	verdict	time	subtask
#1	ACCEPTED	0.00 s	1, 5	details
#2	ACCEPTED	0.00 s	1, 2, 3, 4, 5	details
#3	ACCEPTED	0.03 s	1, 5	details
#4	ACCEPTED	0.02 s	1, 5	details
#5	ACCEPTED	0.02 s	1, 3, 5	details
#6	ACCEPTED	0.02 s	1, 2, 4, 5	details
#7	ACCEPTED	0.02 s	1, 2, 4, 5	details
#8	ACCEPTED	0.02 s	1, 5	details
#9	ACCEPTED	0.03 s	1, 5	details
#10	ACCEPTED	0.02 s	1, 3, 4, 5	details
#11	ACCEPTED	0.02 s	1, 3, 5	details
#12	ACCEPTED	0.02 s	1, 4, 5	details
#13	ACCEPTED	0.02 s	1, 3, 4, 5	details
#14	ACCEPTED	0.02 s	1, 4, 5	details
#15	ACCEPTED	0.02 s	1, 5	details
#16	ACCEPTED	0.02 s	1, 5	details
#17	ACCEPTED	0.02 s	1, 5	details
#18	ACCEPTED	0.03 s	1, 5	details
#19	ACCEPTED	0.42 s	2, 4, 5	details
#20	ACCEPTED	0.37 s	2, 4, 5	details
#21	ACCEPTED	0.40 s	2, 4, 5	details
#22	ACCEPTED	0.60 s	2, 4, 5	details
#23	ACCEPTED	0.75 s	3, 5	details
#24	ACCEPTED	0.75 s	3, 5	details
#25	ACCEPTED	0.75 s	3, 5	details
#26	ACCEPTED	0.60 s	3, 5	details
#27	ACCEPTED	0.56 s	3, 4, 5	details
#28	ACCEPTED	0.45 s	3, 4, 5	details
#29	ACCEPTED	0.46 s	4, 5	details
#30	ACCEPTED	0.46 s	4, 5	details
#31	ACCEPTED	0.62 s	4, 5	details
#32	ACCEPTED	0.62 s	4, 5	details
#33	ACCEPTED	0.63 s	4, 5	details
#34	ACCEPTED	0.47 s	4, 5	details
#35	ACCEPTED	0.78 s	5	details
#36	ACCEPTED	0.78 s	5	details
#37	ACCEPTED	0.77 s	5	details
#38	ACCEPTED	0.77 s	5	details
#39	ACCEPTED	0.81 s	5	details
#40	ACCEPTED	0.81 s	5	details
#41	ACCEPTED	0.70 s	5	details
#42	ACCEPTED	0.77 s	5	details
#43	ACCEPTED	0.78 s	5	details
#44	ACCEPTED	0.80 s	5	details

Code

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef __int128_t i128;
#define all(x) begin(x), end(x)
#define sz(x) ((int)(x).size())
const ll inf = 4e18;

struct union_find {
    vector<ll> lnk, siz;

    union_find(ll n) : lnk(n), siz(n, 1) {
        iota(all(lnk), 0ll);
    }

    ll find(ll a) {
        if (lnk[a] != a) lnk[a] = find(lnk[a]);
        return lnk[a];
    }

    bool merge(ll a, ll b) {
        a = find(a), b = find(b);
        if (a == b) return false;
        if (siz[a] < siz[b]) swap(a, b);
        lnk[b] = a;
        siz[a] += siz[b];
        return true;
    }
};

struct binary_lifting {
    vector<ll> dep;
    vector<vector<ll>> jmp;

    binary_lifting(vector<set<ll>> &adj) {
        ll n = sz(adj);
        dep = vector<ll>(n);
        jmp = vector<vector<ll>>(20, vector<ll>(n));
        auto dfs = [&](auto &oink, ll i, ll p, ll d) -> void {
            jmp[0][i] = p;
            dep[i] = d;
            for (auto &e : adj[i]) {
                if (e == p) continue;
                oink(oink, e, i, d+1);
            }
        };
        dfs(dfs, 0, 0, 0);
        for (ll j = 1; j < 20; j++) {
            for (ll i = 0; i < n; i++) {
                jmp[j][i] = jmp[j-1][jmp[j-1][i]];
            }
        }
    }

    ll lift(ll i, ll k) {
        for (ll j = 20; j--;) {
            if ((1 << j) > k) continue;
            i = jmp[j][i];
            k -= (1 << j);
        }
        return i;
    }

    ll lca(ll a, ll b) {
        if (dep[a] > dep[b]) swap(a, b);
        b = lift(b, dep[b] - dep[a]);
        if (a == b) return a;
        for (ll j = 20; j--;) {
            if (jmp[j][a] == jmp[j][b]) continue;
            a = jmp[j][a], b = jmp[j][b];
        }
        return jmp[0][a];
    }

    ll dist(ll a, ll b) {
        return dep[a] + dep[b] - 2 * dep[lca(a, b)];
    }
};

void solve() {
    ll n, q; cin >> n >> q;
    vector<vector<bool>> grid(n, vector<bool>(n));
    vector<vector<ll>> id(n, vector<ll>(n));
    ll t = 0;
    for (ll i = 0; i < n; i++) {
        for (ll j = 0; j < n; j++) {
            char c; cin >> c;
            grid[i][j] = (c == '#');
            if (!grid[i][j]) continue;
            id[i][j] = t++;
        }
    }

    union_find dsur(t), dsuc(t);
    vector<set<ll>> adjr(t), adjc(t);
    for (ll i = 0; i < n-1; i++) {
        for (ll j = 0; j < n-1; j++) {
            if (!grid[i][j]) continue;
            if (grid[i][j+1]) dsur.merge(id[i][j], id[i][j+1]);
            if (grid[i+1][j]) dsuc.merge(id[i][j], id[i+1][j]);
        }
    }
    for (ll i = 0; i < n-1; i++) {
        for (ll j = 0; j < n-1; j++) {
            if (!grid[i][j]) continue;
            if (grid[i+1][j]) {
                ll u = dsur.find(id[i][j]);
                ll v = dsur.find(id[i+1][j]);
                adjr[u].insert(v);
                adjr[v].insert(u);
            }
            if (grid[i][j+1]) {
                ll u = dsuc.find(id[i][j]);
                ll v = dsuc.find(id[i][j+1]);
                adjc[u].insert(v);
                adjc[v].insert(u);
            }
        }
    }
    binary_lifting lcar(adjr), lcac(adjc);

    while (q--) {
        ll sr, sc, tr, tc;
        cin >> sr >> sc >> tr >> tc;
        sr--; sc--; tr--; tc--;
        ll a = id[sr][sc], b = id[tr][tc];
        cout << lcar.dist(dsur.find(a), dsur.find(b)) + lcac.dist(dsuc.find(a), dsuc.find(b)) << '\n';
    }
}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    solve();
}

Test details

Test 1

Subtask: 1, 5

Verdict: ACCEPTED

input
`8 4 ........ ..####.. .##.###. .##.###. ...` view save

correct output
`5 0 17 3` view save

user output
`5 0 17 3` view save

Test 2

Subtask: 1, 2, 3, 4, 5

Verdict: ACCEPTED

input
`3 1 ... .#. ... 2 2 2 2` view save

correct output
`0` view save

user output
`0` view save

Test 3

Subtask: 1, 5

Verdict: ACCEPTED

input
`199 196 .................................` view save

correct output
`468 605 825 532 496 ...` view save

user output
`468 605 825 532 496 ...` view save

Test 4

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`112 347 142 459 239 ...` view save

user output
`112 347 142 459 239 ...` view save

Test 5

Subtask: 1, 3, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`381 544 94 532 98 ...` view save

user output
`381 544 94 532 98 ...` view save

Test 6

Subtask: 1, 2, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`133 73 81 82 53 ...` view save

user output
`133 73 81 82 53 ...` view save

Test 7

Subtask: 1, 2, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`139 52 101 14 144 ...` view save

user output
`139 52 101 14 144 ...` view save

Test 8

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`236 555 878 632 829 ...` view save

user output
`236 555 878 632 829 ...` view save

Test 9

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`425 296 698 577 422 ...` view save

user output
`425 296 698 577 422 ...` view save

Test 10

Subtask: 1, 3, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`1365 7284 11808 6136 9283 ...` view save

user output
`1365 7284 11808 6136 9283 ...` view save

Test 11

Subtask: 1, 3, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`6292 17954 16728 8938 1335 ...` view save

user output
`6292 17954 16728 8938 1335 ...` view save

Test 12

Subtask: 1, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`27 141 269 127 61 ...` view save

user output
`27 141 269 127 61 ...` view save

Test 13

Subtask: 1, 3, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`19552 19544 19478 19402 19456 ...` view save

user output
`19552 19544 19478 19402 19456 ...` view save

Test 14

Subtask: 1, 4, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`17624 17515 17468 17689 17510 ...` view save

user output
`17624 17515 17468 17689 17510 ...` view save

Test 15

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`1584 1433 567 2248 1030 ...` view save

user output
`1584 1433 567 2248 1030 ...` view save

Test 16

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`5872 6374 60 323 5311 ...` view save

user output
`5872 6374 60 323 5311 ...` view save

Test 17

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`1852 213 252 3861 1835 ...` view save

user output
`1852 213 252 3861 1835 ...` view save

Test 18

Subtask: 1, 5

Verdict: ACCEPTED

input
`200 200 .................................` view save

correct output
`1564 2709 866 1318 1758 ...` view save

user output
`1564 2709 866 1318 1758 ...` view save

Test 19

Subtask: 2, 4, 5

Verdict: ACCEPTED

input
`997 100000 .................................` view save

correct output
`150 531 370 518 508 ...` view save

user output
`150 531 370 518 508 ...` view save

Test 20

Subtask: 2, 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`390 278 783 1269 249 ...` view save

user output
`390 278 783 1269 249 ...` view save

Test 21

Subtask: 2, 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`63 142 813 683 731 ...` view save

user output
`63 142 813 683 731 ...` view save

Test 22

Subtask: 2, 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`949 876 1209 494 1033 ...` view save

user output
`949 876 1209 494 1033 ...` view save

Test 23

Subtask: 3, 5

Verdict: ACCEPTED

input
`997 100000 .................................` view save

correct output
`714 2683 3699 2085 7850 ...` view save

user output
`714 2683 3699 2085 7850 ...` view save

Test 24

Subtask: 3, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`5081 1819 1050 4610 528 ...` view save

user output
`5081 1819 1050 4610 528 ...` view save

Test 25

Subtask: 3, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`3554 6322 6648 2882 1490 ...` view save

user output
`3554 6322 6648 2882 1490 ...` view save

Test 26

Subtask: 3, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`433976 81646 87810 48080 110879 ...` view save

user output
`433976 81646 87810 48080 110879 ...` view save

Test 27

Subtask: 3, 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`207982 140036 208364 51912 56826 ...` view save

user output
`207982 140036 208364 51912 56826 ...` view save

Test 28

Subtask: 3, 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`497525 497563 498000 496804 497335 ...` view save

user output
`497525 497563 498000 496804 497335 ...` view save

Test 29

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`38580 2097 9795 38033 1639 ...` view save

user output
`38580 2097 9795 38033 1639 ...` view save

Test 30

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`33 20900 25028 1782 13599 ...` view save

user output
`33 20900 25028 1782 13599 ...` view save

Test 31

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1421 1122 1840 834 443 ...` view save

user output
`1421 1122 1840 834 443 ...` view save

Test 32

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1378 1751 2274 250 811 ...` view save

user output
`1378 1751 2274 250 811 ...` view save

Test 33

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1126 886 544 223 272 ...` view save

user output
`1126 886 544 223 272 ...` view save

Test 34

Subtask: 4, 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`327286 447779 447534 448307 446997 ...` view save

user output
`327286 447779 447534 448307 446997 ...` view save

Test 35

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`2597 1473 1933 2691 1837 ...` view save

user output
`2597 1473 1933 2691 1837 ...` view save

Test 36

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`553 4357 3147 6951 1573 ...` view save

user output
`553 4357 3147 6951 1573 ...` view save

Test 37

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1723 2039 1871 5638 4256 ...` view save

user output
`1723 2039 1871 5638 4256 ...` view save

Test 38

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1546 704 2796 3802 1870 ...` view save

user output
`1546 704 2796 3802 1870 ...` view save

Test 39

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`3115 2042 2083 3227 740 ...` view save

user output
`3115 2042 2083 3227 740 ...` view save

Test 40

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`5222 3211 5230 1772 2310 ...` view save

user output
`5222 3211 5230 1772 2310 ...` view save

Test 41

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`159214 68851 200821 141404 145704 ...` view save

user output
`159214 68851 200821 141404 145704 ...` view save

Test 42

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`1843 25028 124430 84542 131339 ...` view save

user output
`1843 25028 124430 84542 131339 ...` view save

Test 43

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`111206 75799 12026 142133 20483 ...` view save

user output
`111206 75799 12026 142133 20483 ...` view save

Test 44

Subtask: 5

Verdict: ACCEPTED

input
`1000 100000 .................................` view save

correct output
`20360 9075 12187 54923 54574 ...` view save

user output
`20360 9075 12187 54923 54574 ...` view save

BOI 2026 Mirror Day 1

Island

Code

Test details

Test 1

Test 2

Test 3

Test 4

Test 5

Test 6

Test 7

Test 8

Test 9

Test 10

Test 11

Test 12

Test 13

Test 14

Test 15

Test 16

Test 17

Test 18

Test 19

Test 20

Test 21

Test 22

Test 23

Test 24

Test 25

Test 26

Test 27

Test 28

Test 29

Test 30

Test 31

Test 32

Test 33

Test 34

Test 35

Test 36

Test 37

Test 38

Test 39

Test 40

Test 41

Test 42

Test 43

Test 44

Tasks

Submissions (Sebastian)