49 lines
1.3 KiB
C++
49 lines
1.3 KiB
C++
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struct LCA {
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vector<int> depth;
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vector<vector<int>> pa;
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LCA(const vector<vector<int>>& g, int root = 1) {
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int n = g.size() - 1;
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int m = 32 - __builtin_clz(n);
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depth.resize(n + 1);
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pa.resize(n + 1, vector<int>(m, -1));
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function<void(int, int)> dfs = [&](int x, int fa) {
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pa[x][0] = fa;
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for (int y: g[x]) {
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if (y != fa) {
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depth[y] = depth[x] + 1;
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dfs(y, x);
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}
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}
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};
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dfs(root, 0);
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for (int i = 0; i < m - 1; i++)
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for (int x = 1; x <= n; x++)
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if (int p = pa[x][i]; p != -1)
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pa[x][i + 1] = pa[p][i];
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}
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int get_kth_ancestor(int node, int k) {
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for (; k; k &= k - 1)
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node = pa[node][__builtin_ctz(k)];
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return node;
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}
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int query(int x, int y) {
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if (depth[x] > depth[y])
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swap(x, y);
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y = get_kth_ancestor(y, depth[y] - depth[x]);
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if (y == x)
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return x;
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for (int i = pa[x].size() - 1; i >= 0; i--) {
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int px = pa[x][i], py = pa[y][i];
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if (px != py) {
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x = px;
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y = py;
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}
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}
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return pa[x][0];
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}
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};
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