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  1. // ~~ icebear ~~
  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 "icebear"
  33. #define prev ___prev
  34.  
  35. const int MOD = 1e9 + 7;
  36. const int inf = 1e9 + 27092008;
  37. const ll INF = 1e18 + 27092008;
  38. const int N = 5e5 + 5;
  39. int n, f[N][2][3], c[N], prev[2][3];
  40. vector<int> G[N];
  41. int sumOff[N];
  42.  
  43. // f[u][j][k] : min values to set all subtrees of u, j is state of u after having done,
  44. //                  k is number of children that in important path
  45.  
  46. void dfs(int u, int par) {
  47.     sumOff[u] = (c[u] == 0);
  48.     for(int v : G[u]) if (v != par) {
  49.         dfs(v, u);
  50.         sumOff[u] += sumOff[v];
  51.     }
  52.  
  53.     if (sumOff[u] == 0) return; // useless
  54.     REP(k, 3) f[u][c[u] ^ 1][k] = 1; // base string
  55.  
  56.     for(int v : G[u]) if (v != par && sumOff[v] > 0) {
  57.         REP(j, 2) REP(k, 3) {
  58.             prev[j][k] = f[u][j][k];
  59.             f[u][j][k] = inf;
  60.         }
  61.         REP(j, 2) {
  62.             // first edge doesn't affect to u, v and answer
  63.             minimize(f[u][j][0], prev[j^1][0] + f[v][1][0] + 1); // u -> v -> [u]
  64.             minimize(f[u][j][0], prev[j][0] + f[v][0][0] + 3); // u -> v -> [u -> v -> u]
  65.  
  66.             minimize(f[u][j][1], prev[j][0] + f[v][1][1]); // v -> u
  67.             minimize(f[u][j][1], prev[j^1][0] + f[v][0][1] + 2); // v -> u -> [v -> u]
  68.             minimize(f[u][j][1], prev[j^1][1] + f[v][1][0] + 1); // u -> v -> [u]
  69.             minimize(f[u][j][1], prev[j][1] + f[v][0][0] + 3); // u -> v -> [u -> v -> u]
  70.  
  71.             minimize(f[u][j][2], prev[j^1][0] + f[v][1][2] + 3); // v -> u -> [v -> u -> v]
  72.             minimize(f[u][j][2], prev[j][0] + f[v][0][2] + 1); // v -> u -> [v]
  73.             minimize(f[u][j][2], prev[j][1] + f[v][1][1]); // u -> v
  74.             minimize(f[u][j][2], prev[j^1][1] + f[v][0][1] + 2); // u -> v -> [u -> v]
  75.             minimize(f[u][j][2], prev[j^1][2] + f[v][1][0] + 1); // u -> v -> [u]
  76.             minimize(f[u][j][2], prev[j][2] + f[v][0][0] + 3); // u -> v -> [u -> v -> u]
  77.         }
  78.  
  79.         REP(j, 2) {
  80.             minimize(f[u][j][1], f[u][j][0]);
  81.             minimize(f[u][j][2], f[u][j][1]);
  82.         }
  83.     }
  84. }
  85.  
  86. void init(void) {
  87.     cin >> n;
  88.     FOR(i, 1, n) {
  89.         char x; cin >> x;
  90.         c[i] = (x == '1');
  91.     }
  92.     FOR(i, 2, n) {
  93.         int u, v;
  94.         cin >> u >> v;
  95.         G[u].pb(v);
  96.         G[v].pb(u);
  97.     }
  98. }
  99.  
  100. void process(void) {
  101.     memset(f, 0x3f, sizeof f);
  102.     FOR(i, 1, n) if (c[i] == 0) {
  103.         dfs(i, -1);
  104.         cout << f[i][1][2] << '\n';
  105.         break;
  106.     }
  107. }
  108.  
  109. int main() {
  110.     ios_base::sync_with_stdio(0);
  111.     cin.tie(0); cout.tie(0);
  112.     if (fopen(task".inp", "r")) {
  113.         freopen(task".inp", "r", stdin);
  114.         freopen(task".out", "w", stdout);
  115.     }
  116.     int tc = 1;
  117. //    cin >> tc;
  118.     while(tc--) {
  119.         init();
  120.         process();
  121.     }
  122.     return 0;
  123. }
  124.  
Success #stdin #stdout 0.01s 29464KB
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https://ideone.com/LJsw3I
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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