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  1. // ~~ icebear love attttt ~~
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. typedef long long ll;
  6. typedef pair<int, int> ii;
  7. typedef pair<int, ii> iii;
  8.  
  9. template<class T>
  10.     bool minimize(T &a, const T &b) {
  11.         if (a > b) return a = b, true;
  12.         return false;
  13.     }
  14.  
  15. template<class T>
  16.     bool maximize(T &a, const T &b) {
  17.         if (a < b) return a = b, true;
  18.         return false;
  19.     }
  20.  
  21. #define FOR(i,a,b) for(int i=(a); i<=(b); ++i)
  22. #define FORR(i,a,b) for(int i=(a); i>=(b); --i)
  23. #define REP(i, n) for(int i=0; i<(n); ++i)
  24. #define RED(i, n) for(int i=(n)-1; i>=0; --i)
  25. #define MASK(i) (1LL << (i))
  26. #define BIT(S, i) (((S) >> (i)) & 1)
  27. #define mp make_pair
  28. #define pb push_back
  29. #define fi first
  30. #define se second
  31. #define all(x) x.begin(), x.end()
  32. #define task "icebearat"
  33.  
  34. const int MOD = 1e9 + 7;
  35. const int inf = 1e9 + 27092008;
  36. const ll INF = 1e18 + 27092008;
  37. const int N = 3e5 + 5;
  38. int n, k, cnt;
  39. bool bom[N], have[N];
  40. vector<int> G[N], adj[N];
  41.  
  42. /**
  43. 	f[u] : min dist to a bom in subtree u
  44. 	g[u] : max dist to a node which is parent of a bom in subtree u
  45. */
  46.  
  47. void dfs(int u, int par) {
  48.     for(int v : G[u]) if (v != par) {
  49.         dfs(v, u);
  50.         if (have[v]) {
  51.             adj[u].pb(v);
  52.             adj[v].pb(u);
  53.         }
  54.         have[u] |= have[v];
  55.     }
  56. }
  57.  
  58. ii DFS(int u, int par, const int limit) {
  59.     int f = inf, g = -inf;
  60.     for(int v : adj[u]) if (v != par) {
  61.         ii tmp = DFS(v, u, limit);
  62.         minimize(f, tmp.fi + 1);
  63.         maximize(g, tmp.se + 1);
  64.     }
  65.     if (cnt > k) return mp(0, 0);
  66.     if (bom[u] && f > limit) // now calculate, dist = 2 * limit
  67.         maximize(g, 0);
  68.     if (f + g <= limit) // a node choose at f[u] is good enough
  69.         g = -inf;
  70.     if (g == limit) {
  71.         cnt++;
  72.         f = 0;
  73.         g = -inf;
  74.     }
  75.     return mp(f, g);
  76. }
  77.  
  78. bool check(int limit) {
  79.     cnt = 0;
  80.     int g = DFS(1, -1, limit).se;
  81.     if (g >= 0) cnt++;
  82.     return (cnt <= k);
  83. }
  84.  
  85. void init(void) {
  86.     cin >> n >> k;
  87.     FOR(i, 1, n) {
  88.         cin >> bom[i];
  89.         have[i] = bom[i];
  90.     }
  91.     FOR(i, 2, n) {
  92.         int u, v;
  93.         cin >> u >> v;
  94.         G[u].pb(v);
  95.         G[v].pb(u);
  96.     }
  97. }
  98.  
  99. void process(void) {
  100.     dfs(1, -1);
  101.     int low = 0, high = n - 1, res = n;
  102.     while(low <= high) {
  103.         int mid = (low + high) >> 1;
  104.         if (check(mid)) res = mid, high = mid - 1;
  105.         else low = mid + 1;
  106.     }
  107.     cout << res;
  108. }
  109.  
  110. int main() {
  111.     ios_base::sync_with_stdio(0);
  112.     cin.tie(0); cout.tie(0);
  113.     if (fopen(task".inp", "r")) {
  114.         freopen(task".inp", "r", stdin);
  115.         freopen(task".out", "w", stdout);
  116.     }
  117.     int tc = 1;
  118. //    cin >> tc;
  119.     while(tc--) {
  120.         init();
  121.         process();
  122.     }
  123.     return 0;
  124. }
  125.  
  126.  
Success #stdin #stdout 0.01s 17604KB
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https://ideone.com/gsWnJI
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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