Submission #526220

#	Time	Username	Problem	Language	Result	Execution time	Memory
526220		mjhmjh1104	Mountains and Valleys (CCO20_day1problem3)	C++17	0 / 25	27 ms	39288 KiB

Main

#include <cstdio>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;

struct Item {
    int posde;
    int negde;
    int ans;
    Item () {}
    Item (int posde, int negde, int ans): posde(posde), negde(negde), ans(ans) {}
} sp_split[19][500000];

int lt_depth[500000][3], lt_dist[500000][3];

void push(int *v, int x) {
    auto t = min_element(v, v + 3);
    if (x > *t) *t = x;
}

void pop(int *v, int x) {
    *find(v, v + 3, x) = 0;
}

int first(int *v) {
    return *max_element(v, v + 3);
}

int second(int *v) {
    return v[0] + v[1] + v[2] - *min_element(v, v + 3);
}

int n, m;
vector<int> tree[500000], child[500000];
vector<pair<int, int>> adj[500000];
int depth[500000], sp[19][500000], sp_dist[19][500000];
int max_depth[500000], rev_max_depth[500000], dist[500000], rev_dist[500000];
int prev_dist[500000], prev_depth[500000][2];

int dfs_dist(int x) {
    max_depth[x] = 0;
    dist[x] = 0;
    int mx0 = (int)-1e9, mx1 = (int)-1e9;
    for (auto &i: child[x]) {
        int t = dfs_dist(i) + 1;
        max_depth[x] = max(max_depth[x], t);
        if (t > mx0) mx1 = mx0, mx0 = t;
        else if (t > mx1) mx1 = t;
        dist[x] = max(dist[x], dist[i]);
    }
    dist[x] = max(dist[x], mx0 + max(mx1, 0));
    return max_depth[x];
}

void dfs_rev_dist(int x) {
    for (auto &i: child[x]) {
        push(lt_depth[x], max_depth[i] + 1);
        if (prev_depth[x][0] < max_depth[i] + 1) prev_depth[x][1] = prev_depth[x][0], prev_depth[x][0] = max_depth[i] + 1;
        else if (prev_depth[x][1] < max_depth[i] + 1) prev_depth[x][1] = max_depth[i] + 1;
        push(lt_dist[x], dist[i]);
        if (prev_dist[x] < dist[i]) prev_dist[x] = dist[i];
    }
    for (auto &i: child[x]) {
        pop(lt_depth[x], max_depth[i] + 1);
        pop(lt_dist[x], dist[i]);
        rev_dist[i] = max({ rev_max_depth[i] = max(first(lt_depth[x]), rev_max_depth[x]) + 1, second(lt_depth[x]), first(lt_depth[x]) + rev_dist[x]});
        push(lt_depth[x], max_depth[i] + 1);
        push(lt_dist[x], dist[i]);
    }
    for (auto &i: child[x]) dfs_rev_dist(i);
}

void dfs_construct(int x) {
    for (auto &i: child[x]) {
        pop(lt_dist[x], dist[i]);
        sp_dist[0][i] = first(lt_dist[x]);
        push(lt_dist[x], dist[i]);
        pop(lt_depth[x], max_depth[i] + 1);
        int V = first(lt_depth[x]);
        sp_dist[0][i] = max(sp_dist[0][i], second(lt_depth[x]));
        sp_split[0][i].posde = V + depth[x];
        sp_split[0][i].negde = V - depth[x];
        push(lt_depth[x], max_depth[i] + 1);
    }
    for (auto &i: child[x]) dfs_construct(i);
}

void dfs_child(int x, int prev = -1) {
    sp[0][x] = prev;
    for (auto &i: tree[x]) if (i != prev) {
        depth[i] = depth[x] + 1;
        child[x].push_back(i);
        dfs_child(i, x);
    }
}

int A, B;

inline int lca(int u, int v) {
    bool sw = false;
    if (depth[u] < depth[v]) swap(u, v), sw = true;
    int diff = depth[u] - depth[v] - 1;
    if (~diff) {
        for (int t = 18; t >= 0; t--) if (diff >= 1 << t) {
            diff -= 1 << t;
            u = sp[t][u];
        }
        if (sw) B = u;
        else A = u;
        u = sp[0][u];
        if (u == v) return u;
    }
    for (int t = 18; t >= 0; t--) if (sp[t][u] != -1 && sp[t][v] != -1 && sp[t][u] != sp[t][v]) {
        u = sp[t][u];
        v = sp[t][v];
    }
    A = u, B = v;
    if (sw) swap(A, B);
    return sp[0][u];
}

int main() {
    scanf("%d%d", &n, &m);
    while (m--) {
        int x, y, w;
        scanf("%d%d%d", &x, &y, &w);
        if (w == 1) {
            tree[x].push_back(y);
            tree[y].push_back(x);
        } else adj[x].push_back({ y, w });
    }
    for (int i = 0; i < n; i++) prev_dist[i] = prev_depth[i][0] = prev_depth[i][1] = (int)-1e9;
    dfs_child(0);
    dfs_dist(0);
    dfs_rev_dist(0);
    dfs_construct(0);
    for (int t = 1; t < 19; t++) for (int i = 0; i < n; i++) {
        if (sp[t - 1][i] == -1) {
            sp[t][i] = -1;
            sp_dist[t][i] = sp_dist[t - 1][i];
            sp_split[t][i] = sp_split[t - 1][i];
        } else {
            sp[t][i] = sp[t - 1][sp[t - 1][i]];
            sp_dist[t][i] = max(sp_dist[t - 1][i], sp_dist[t - 1][sp[t - 1][i]]);
            sp_split[t][i].ans = max({ sp_split[t - 1][sp[t - 1][i]].ans, sp_split[t - 1][i].ans, sp_split[t - 1][sp[t - 1][i]].posde + sp_split[t - 1][i].negde });
            sp_split[t][i].posde = max(sp_split[t - 1][sp[t - 1][i]].posde, sp_split[t - 1][i].posde);
            sp_split[t][i].negde = max(sp_split[t - 1][sp[t - 1][i]].negde, sp_split[t - 1][i].negde);
        }
    }
    int res = 2 * (n - 1) - dist[0];
    for (int i = 0; i < n; i++) for (auto [ j, w ]: adj[i]) {
        A = B = -1;
        int l = lca(i, j);
        int ds = depth[i] + depth[j] - depth[l] - depth[l];
        int curr = w + 2 * (n - 1) - ds - 1;
        int G = 0, y = 0;
        if (A != -1) pop(lt_depth[l], max_depth[A] + 1);
        if (B != -1) pop(lt_depth[l], max_depth[B] + 1);
        if (A != -1) pop(lt_dist[l], dist[A]);
        if (B != -1) pop(lt_dist[l], dist[B]);
        G = first(lt_depth[l]);
        y = max({ y, G + rev_max_depth[l] - 1, second(lt_depth[l]) - 1, first(lt_dist[l]) - 1 });
        if (A != -1) push(lt_depth[l], max_depth[A] + 1);
        if (B != -1) push(lt_depth[l], max_depth[B] + 1);
        if (A != -1) push(lt_dist[l], dist[A]);
        if (B != -1) push(lt_dist[l], dist[B]);
        Item first = { i == l ? (int)-1e9 : prev_depth[i][0] + depth[i], i == l ? (int)-1e9 : prev_depth[i][0] - depth[i], (int)-1e9 };
        Item second = { j == l ? (int)-1e9 : prev_depth[j][0] + depth[j], j == l ? (int)-1e9 : prev_depth[j][0] - depth[j], (int)-1e9 };
        if (i != l) {
            y = max({ y, prev_depth[i][0] + prev_depth[i][1] - 1, prev_dist[i] - 1 });
            first.posde = prev_depth[i][0] + depth[i];
            first.negde = prev_depth[i][0] - depth[i];
        }
        if (j != l) {
            y = max({ y, prev_depth[j][0] + prev_depth[j][1] - 1, prev_dist[j] - 1 });
            second.posde = prev_depth[j][0] + depth[j];
            second.negde = prev_depth[j][0] - depth[j];
        }
        int I = i, J = j;
        for (int t = 18; t >= 0; t--) {
            if (sp[t][I] != -1 && depth[sp[t][I]] > depth[l]) {
                y = max(y, sp_dist[t][I] - 1);
                first.ans = max({ sp_split[t][I].ans, first.ans, sp_split[t][I].posde + first.negde });
                first.posde = max(sp_split[t][I].posde, first.posde);
                first.negde = max(sp_split[t][I].negde, first.negde);
                I = sp[t][I];
            }
            if (sp[t][J] != -1 && depth[sp[t][J]] > depth[l]) {
                y = max(y, sp_dist[t][J] - 1);
                second.ans = max({ sp_split[t][J].ans, first.ans, sp_split[t][J].posde + first.negde });
                second.posde = max(sp_split[t][J].posde, first.posde);
                second.negde = max(sp_split[t][J].negde, first.negde);
                J = sp[t][J];
            }
        }
        int Alt = first.negde + depth[l];
        int Brt = second.negde + depth[l];
        int Lt = max(rev_max_depth[l], G);
        res = min(res, curr - max({ y, Alt + max(Brt, Lt) + 1, max(Alt, Lt) + Brt + 1, first.ans + 1, second.ans + 1, rev_dist[l] - 1 }));
    }
    printf("%d", res);
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:124:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  124 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:127:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  127 |         scanf("%d%d%d", &x, &y, &w);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 1
• Subtask 2: 0 / 2
• Subtask 3: 0 / 2
• Subtask 4: 0 / 6
• Subtask 5: 0 / 2
• Subtask 6: 0 / 3
• Subtask 7: 0 / 5
• Subtask 8: 0 / 4