Submission #755364

#	Time	Username	Problem	Language	Result	Execution time	Memory
755364		wii	Race (IOI11_race)	C++17	0 / 100	4 ms	4948 KiB

race

#include <bits/stdc++.h>
#include "race.h"

using namespace std;

const int Lim = 1e6 + 5;
const int maxn = 2e5 + 5;
const int Inf = 1e9 + 7;
typedef pair<int, int> pii;

template<class T> bool minimize(T &res, const T &x) { if (x < res) { res = x; return true; } return false; }

int n, k;
vector<pii> adj[maxn];
int ans[Lim];

int sz[maxn], f[maxn];
int dfs_sz(int u, int p) {
    sz[u] = 1;
    for (auto [v, w]: adj[u]) if (v != p && !f[v]) {
        sz[u] += dfs_sz(v, u);
    }
    return sz[u];
}

int find_centroid(int u, int p, int n) {
    for (auto [v, w]: adj[u]) if (v != p && !f[v])
        if (sz[v] * 2 > n) return find_centroid(v, u, n);
    return u;
}

int dp[maxn], dist[maxn], dep[maxn];
void add(int u) {
    minimize(dp[dist[u]], dep[u]);
}

void sub(int u) {
    dp[dist[u]] = Inf;
}

void push(int u, int p) {
    if (dist[u] > k) return;

    add(u);
    for (auto [v, w]: adj[u]) if (v != p && !f[v])
        push(v, u);
}

int get(int u, int p) {
    if (dist[u] > k) return Inf;

    int ans = dp[k - dist[u]] + dep[u];
    for (auto [v, w]: adj[u]) if (v != p && !f[v])
        minimize(ans, get(v, u));
    return ans;
}

void pop(int u, int p) {
    if (dist[u] > k) return;

    sub(u);
    for (auto [v, w]: adj[u]) if (v != p && !f[v])
        pop(v, u);
}

void fill(int u, int p) {
    if (p == -1) {
        dist[u] = 0; dep[u] = 0;
    }

    for (auto [v, w]: adj[u]) if (v != p && !f[v]) {
        dist[v] = dist[u] + w;
        dep[v] = dep[u] + 1;

        fill(v, u);
    }
}

int calc(int r) {
    fill(r, -1);

    int ans = Inf;
    add(r);

    for (auto [u, w]: adj[r]) {
        minimize(ans, get(u, r));
        push(u, r);
    }

    pop(r, -1);
    return ans;
}

int centroid(int u) {
    int n = dfs_sz(u, -1);
    u = find_centroid(u, -1, n);

    int ans = calc(u);

    f[u] = true;
    for (auto [v, w]: adj[u]) if (!f[v])
        ans = min(ans, centroid(v));
    f[u] = false;

    return ans;
}

int best_path(int N, int K, int H[][2], int L[]) {
    n = N; k = K;
    for (int i = 0; i < n - 1; ++i) {
        int u = H[i][0];
        int v = H[i][1];
        int w = L[i];

        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }

    for (int i = 0; i <= k; ++i) dp[i] = Inf;
    int ans = centroid(0);

    if (ans > n) ans = -1;
    return ans;
}

// #define testing
#ifdef testing

#define MAX_N 500000

static int N, K;
static int H[MAX_N][2];
static int L[MAX_N];
static int solution;

inline
void my_assert(int e) {if (!e) abort();}

void read_input()
{
  int i;
  my_assert(2==scanf("%d %d",&N,&K));
  for(i=0; i<N-1; i++)
    my_assert(3==scanf("%d %d %d",&H[i][0],&H[i][1],&L[i]));
  my_assert(1==scanf("%d",&solution));
}

int main()
{
  int ans;
  read_input();
  ans = best_path(N,K,H,L);
  if(ans==solution)
    printf("Correct.\n");
  else
    printf("Incorrect. Returned %d, Expected %d.\n",ans,solution);

  return 0;
}

#endif // testing

/**
4 3
0 1 1
1 2 2
1 3 4
2

3 3
0 1 1
1 2 1
-1

11 12
0 1 3
0 2 4
2 3 5
3 4 4
4 5 6
0 6 3
6 7 2
6 8 5
8 9 6
8 10 7
2


**/

• Subtask 1: 0 / 9
• Subtask 2: 0 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57