2020牛客多校第一场B(虚树)
#include<cstdio>
typedef long long ll;
const int N = 2e5 + 50;
int n, cnt, top, tot;
int c[N], mindiv[N], dep[N], w[N];
int head[N], sta[N], lca_dep[N];
ll minn, ans[N];
struct Edge{
int nex, to;
}e[N << 1];
inline int lowbit(int &x) { return x & -x; }
inline ll min(ll a, ll b) { return a < b ? a : b; }
inline void add(int a, int b) { e[++cnt] = {head[a], b}; head[a] = cnt; }
void add(int x){
while(x <= n){
++c[x];
x += lowbit(x);
}
}
int ask(int x){
int ans = 0;
while(x){
ans += c[x];
x -= lowbit(x);
}
return ans;
}
void init(int n){
cnt = 0;
for(int i = 1; i <= n; ++i) c[i] = w[i] = dep[i] = lca_dep[i] = ans[i] = 0;
}
void pre(int n){
for(int i = 2; i <= n; ++i)
for(int t = i; t <= n; t += i)
if(!mindiv[t]) mindiv[t] = i;
}
void build(){
tot = n;
sta[top = 1] = 1, head[1] = 0;
for(int i = 2, t; i <= n; ++i){
t = i; dep[i] = dep[i - 1] + 1;
while(t != mindiv[t]) ++dep[i], t /= mindiv[t];
lca_dep[i] = ask(n) - ask(t - 1);
for(int t = i; t != 1; t /= mindiv[t]) add(mindiv[t]);
}
for(int i = 2; i <= n; ++i){
//printf("%d %d\n", lca_dep[i], sta[1]);
while(top > 1 && dep[sta[top - 1]] >= lca_dep[i]){
add(sta[top - 1], sta[top]);
--top;
}
if(dep[sta[top]] != lca_dep[i]){
dep[++tot] = lca_dep[i];
head[tot] = 0;
add(tot, sta[top]);
sta[top] = tot;
}
head[i] = 0, sta[++top] = i;
}
//printf("%d %d ", top, sta[1]);
for(int i = 1; i < top; ++i) add(sta[i], sta[i + 1]);
}
void dfs(int u){
//printf("%d ", u);
ans[1] += 1LL * w[u] * dep[u];
for(int i = head[u]; i; i = e[i].nex){
int to = e[i].to;
dfs(to);
w[u] += w[to];
}
}
void dfs2(int u){
for(int i = head[u]; i; i = e[i].nex){
int to = e[i].to;
ans[to] = ans[u] + (w[1] - 2LL * w[to]) * (dep[to] - dep[u]);
dfs2(to);
}
}
int main(){
pre(1e5);
while(scanf("%d", &n) != EOF){
for(int i = 1; i <= n; ++i) scanf("%d", &w[i]);
minn = 1e15;
build();
dfs(1); dfs2(1);
for(int i = 1; i <= tot; ++i) minn = min(ans[i], minn);
printf("%lld\n", minn);
init(tot);
}
return 0;
}
你只有十分努力,才能看上去毫不费力。