73 lines
2.0 KiB
C++
73 lines
2.0 KiB
C++
#include <vector>
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#include <bit>
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#include <bitset>
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#include <cstdint>
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class TreeAncestor {
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private:
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std::vector<std::vector<int>> predecessor;
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std::vector<int> depth;
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public:
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TreeAncestor(std::vector<std::pair<int, int>>& edges) {
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int n = edges.size() + 1;
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int m = bit_width((unsigned)n);
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predecessor.resize(n, std::vector<int>(m, -1));
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depth.resize(n, 0);
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std::vector<std::vector<int>> graph(n);
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for (const auto& [u, v] : edges) {
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graph[u].emplace_back(v);
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graph[v].emplace_back(u);
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}
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auto dfs = [&](auto&& dfs, int x, int fa) -> void {
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predecessor[x][0] = fa;
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for (auto y : graph[x]) {
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if (y != fa) {
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depth[y] = depth[x] + 1;
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dfs(dfs, y, x);
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}
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}
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};
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dfs(dfs, 0, -1);
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for (int i = 1; i < m; i++) {
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for (int x = 0; x < n; x++) {
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if (int p = predecessor[x][i - 1]; p != -1) {
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predecessor[x][i] = predecessor[p][i - 1];
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}
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}
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}
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}
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int getKthAncestor(int node, int k) {
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//for (int i = 0; i < bit_width((unsigned)k) && node != -1; i++) {
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// if (k >> i & 1) {
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// node = predecessor[node][i];
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// }
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//}
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for (; k && node != -1; k &= k - 1) {
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node = predecessor[node][countr_zero(unsigned(k))];
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}
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return node;
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}
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int getLowestCommonAncestor(int u, int v) {
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if (depth[u] > depth[v]) {
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std::swap(u, v);
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}
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for (int k = depth[v] - depth[u]; k; k &= k - 1) {
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v = predecessor[v][countr_zero(unsigned(k))];
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}
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if (u != v) {
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for (int i = predecessor[u].size() -1; i >= 0; i--) {
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int pu = predecessor[u][i], pv = predecessor[v][i];
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if (pu != pv) {
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u = pu, v = pv;
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}
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}
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}
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return predecessor[u][0];
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}
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}; |