CF1009F Dominant Indices [线段树合并]

Posted 2022-07-08 qq62c30ac77b2a7

​​传送门​​

， 听说可以长链剖分，但是不会啊！

因为我们要维护每个点子树为 dep 的个数，考虑线段树合并，将子树的dep信息合并到父亲

所以以dep为下标建立线段树，然后线段树维护区间最大值，也就是查dep出现次数最多的点

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#include<bits/stdc++.h>
#define N 1000050
using namespace std;
int first[N], nxt[N<<1], to[N<<1], tot;
void add(int x, int y)
  nxt[++tot] = first[x], first[x] = tot, to[tot] = y;

int n, dep[N], ans[N], res;
int rt[N], Max[N * 22], ls[N * 22], rs[N * 22], id[N * 22];
void Pushup(int x)
  if(Max[ls[x]] >= Max[rs[x]]) Max[x] = Max[ls[x]]; id[x] = id[ls[x]];
  else Max[x] = Max[rs[x]]; id[x] = id[rs[x]];

void Insert(int &x, int l, int r, int p)
  if(!x) x = ++res; 
  if(l == r)  Max[x]++; id[x] = l; return;
  int mid = (l+r) >> 1;
  if(p <= mid) Insert(ls[x], l, mid, p);
  else Insert(rs[x], mid+1, r, p); Pushup(x);
 
int Merge(int x, int y, int l, int r)
  if(!x || !y) return x + y;
  if(l == r) Max[x] += Max[y]; id[x] = l; return x;
  int mid = (l+r) >> 1;
  ls[x] = Merge(ls[x], ls[y], l, mid);
  rs[x] = Merge(rs[x], rs[y], mid+1, r);
  Pushup(x); return x; 

void dfs(int u, int fa)
  Insert(rt[u], 1, n, dep[u]);
  for(int i=first[u];i;i=nxt[i])
    int t = to[i]; if(t == fa) continue;
    dep[t] = dep[u] + 1; dfs(t, u);
    rt[u] = Merge(rt[u], rt[t], 1, n);
   ans[u] = id[rt[u]] - dep[u];

int main() 
  Max[0] = -1e9;
  scanf("%d", &n);
  for(int i=1; i<n; i++)
    int x, y; scanf("%d%d", &x, &y); 
    add(x, y); add(y, x);
   dep[1] = 1; dfs(1, 0);
  for(int i=1; i<=n; i++) printf("%d\\n", ans[i]);
  return 0;