牛客国庆集训派对Day3 B Tree

Tree

思路:

树形dp

注意0不存在逆元,任何一个数乘以0就变成0了,就没有价值浪,所以要暴力转移

代码:

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
//#define mp make_pair
#define pb push_back
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pli pair<LL, int>
#define pii pair<int, int>
#define piii pair<pli, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);
//head const int N = 1e6 + ;
const int MOD = 1e9 + ;
struct edge {
int to;
int next;
}edge[N*];
LL cnt[N], _cnt[N];
int head[N], tot = ;
void add_edge(int u, int v) {
edge[tot].to = v;
edge[tot].next = head[u];
head[u] = tot++;
}
LL q_pow(LL n, LL k) {
LL ans = ;
while(k) {
if(k&) ans = (ans * n) % MOD;
n = (n * n) % MOD;
k >>= ;
}
return ans;
}
void dfs(int o, int u) {
cnt[u] = ;
for (int i = head[u]; ~i; i = edge[i].next) {
int v = edge[i].to;
if(v != o) {
dfs(u, v);
cnt[u] = (cnt[u] * (cnt[v]+)) % MOD;
}
}
}
void DFS(int o, int u) {
for (int i = head[u]; ~i; i = edge[i].next) {
int v = edge[i].to;
if(v != o) {
LL t = ;
if(cnt[v]+ != MOD) t = (cnt[u] * q_pow(cnt[v]+, MOD-)) % MOD;
else {
for (int i = head[u]; ~i; i = edge[i].next) {
int vv = edge[i].to;
if(vv != o && vv != v) {
t = (t * (cnt[vv]+)) % MOD;
}
}
}
_cnt[v] = (_cnt[u]*t + ) % MOD;
DFS(u, v);
}
}
}
int main() {
int n, u, v;
scanf("%d", &n);
for (int i = ; i <= n; i++) head[i] = -;
for (int i = ; i < n; i++) {
scanf("%d %d", &u, &v);
add_edge(u, v);
add_edge(v, u);
}
dfs(, );
_cnt[] = ;
DFS(, );
for (int i = ; i <= n; i++) {
printf("%lld\n", (cnt[i] * _cnt[i]) % MOD);
}
return ;
}
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