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P3379 【模板】最近公共祖先（LCA）

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https://www.luogu.com.cn/record/94730020
This commit is contained in:
Baoshuo Ren 2022-11-20 09:14:14 +08:00
parent 777fd68b87
commit ef8275fc7a
Signed by: baoshuo
GPG Key ID: 00CB9680AB29F51A
1 changed files with 5 additions and 4 deletions
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9
Luogu/P3379/P3379.cpp
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@ -10,13 +10,14 @@ const char endl = '\n';
const int N = 5e5 + 5; const int N = 5e5 + 5;
const int INF = 0x3f3f3f3f; const int INF = 0x3f3f3f3f;
int n, m, s, dep[N], fa[N][25]; int n, m, s, dep[N], fa[N][std::__lg(N) + 1];
std::vector<int> g[N]; std::vector<int> g[N];
void bfs(int s) { void bfs(int s) {
std::fill_n(dep, N, INF); std::fill_n(dep, N, INF);
std::queue<int> q; std::queue<int> q;
q.emplace(s); q.emplace(s);
dep[0] = 0; dep[0] = 0;
dep[s] = 1; dep[s] = 1;
@ -31,7 +32,7 @@ void bfs(int s) {
q.emplace(v); q.emplace(v);
fa[v][0] = u; fa[v][0] = u;
for (int k = 1; k <= 19; k++) { for (int k = 1; k <= std::__lg(n); k++) {
fa[v][k] = fa[fa[v][k - 1]][k - 1]; fa[v][k] = fa[fa[v][k - 1]][k - 1];
} }
} }
@ -42,7 +43,7 @@ void bfs(int s) {
int lca(int x, int y) { int lca(int x, int y) {
if (dep[x] < dep[y]) std::swap(x, y); if (dep[x] < dep[y]) std::swap(x, y);
for (int k = 19; k >= 0; k--) { for (int k = std::__lg(n); k >= 0; k--) {
if (dep[fa[x][k]] >= dep[y]) { if (dep[fa[x][k]] >= dep[y]) {
x = fa[x][k]; x = fa[x][k];
} }
@ -50,7 +51,7 @@ int lca(int x, int y) {
if (x == y) return x; if (x == y) return x;
for (int k = 19; k >= 0; k--) { for (int k = std::__lg(n); k >= 0; k--) {
if (fa[x][k] != fa[y][k]) { if (fa[x][k] != fa[y][k]) {
x = fa[x][k]; x = fa[x][k];
y = fa[y][k]; y = fa[y][k];