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| 1 | +<snippet> |
| 2 | + <content><![CDATA[ |
| 3 | +struct Segtree { |
| 4 | +private: |
| 5 | + int n; |
| 6 | + vector <pii> tr; |
| 7 | + pii neutral_tr = {INT_MAX, 0}; |
| 8 | +
|
| 9 | + pii merge(pii a, pii b) { |
| 10 | + if (a.fs < b.fs) |
| 11 | + return a; |
| 12 | + else |
| 13 | + return b; |
| 14 | + } |
| 15 | +
|
| 16 | + void build(const vector <pii>& a) { |
| 17 | + forn (i, 0, n) |
| 18 | + tr[i + n] = a[i]; |
| 19 | + for (int i = n - 1; i > 0; i--) |
| 20 | + tr[i] = merge(tr[2 * i], tr[2 * i + 1]); |
| 21 | + } |
| 22 | +public: |
| 23 | + Segtree(const vector <pii>& a) { |
| 24 | + n = sz(a); |
| 25 | + tr.resize(2 * n, neutral_tr); |
| 26 | + build(a); |
| 27 | + } |
| 28 | +
|
| 29 | + pii get(int l, int r) { |
| 30 | + pii ans = neutral_tr; |
| 31 | + for (l += n, r += n; l < r; l /= 2, r /= 2) { |
| 32 | + if (l % 2) |
| 33 | + ans = merge(ans, tr[l++]); |
| 34 | + if (r % 2) |
| 35 | + ans = merge(ans, tr[--r]); |
| 36 | + } |
| 37 | + return ans; |
| 38 | + } |
| 39 | +}; |
| 40 | +
|
| 41 | +vector <int> first; |
| 42 | +vector <pii> euler; |
| 43 | +
|
| 44 | +void dfs(int v, int p, int cur_h, const vector <vector <int>>& gr) { |
| 45 | + first[v] = sz(euler); |
| 46 | + euler.eb(cur_h, v); |
| 47 | + for (int u : gr[v]) { |
| 48 | + if (u != p) { |
| 49 | + dfs(u, v, cur_h + 1, gr); |
| 50 | + euler.eb(cur_h, v); |
| 51 | + } |
| 52 | + } |
| 53 | +} |
| 54 | +
|
| 55 | +int lca(int v, int u, Segtree& a) { |
| 56 | + if (first[v] > first[u]) |
| 57 | + swap(v, u); |
| 58 | + return a.get(first[v], first[u] + 1).sc; |
| 59 | +} |
| 60 | +
|
| 61 | +]]></content> |
| 62 | + <!-- Optional: Set a tabTrigger to define how to trigger the snippet --> |
| 63 | + <tabTrigger>lca</tabTrigger> |
| 64 | + <!-- Optional: Set a scope to limit where the snippet will trigger --> |
| 65 | + <!-- <scope>source.python</scope> --> |
| 66 | +</snippet> |
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