結果

問題 No.1333 Squared Sum
ユーザー toyuzukotoyuzuko
提出日時 2021-04-17 23:48:04
言語 PyPy3
(7.3.15)
結果
AC  
実行時間 1,198 ms / 2,000 ms
コード長 2,361 bytes
コンパイル時間 156 ms
コンパイル使用メモリ 82,368 KB
実行使用メモリ 205,004 KB
最終ジャッジ日時 2024-07-04 04:20:46
合計ジャッジ時間 30,772 ms
ジャッジサーバーID
（参考情報） 		judge4 / judge5
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ファイルパターン 結果
other AC * 44
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ソースコード

diff # 

class Tree():
    def __init__(self, n):
        self.n = n
        self.tree = [[] for _ in range(n)]
        self.root = None

    def add_edge(self, u, v, c):
        if u > v: u, v = v, u
        self.tree[u].append((v, c))
        self.tree[v].append((u, c))

    def set_root(self, r=0):
        self.root = r
        self.par = [None] * self.n
        self.ord = [r]
        self.cost = [0] * N
        stack = [r]
        while stack:
            v = stack.pop()
            for adj, cost in self.tree[v]:
                if self.par[v] == adj: continue
                self.cost[adj] = cost
                self.par[adj] = v
                self.ord.append(adj)
                stack.append(adj)

    def rerooting(self, op, e, merge, id):
        if self.root is None: self.set_root()
        dp = [e] * self.n
        lt = [id] * self.n
        rt = [id] * self.n
        inv = [id] * self.n
        for v in self.ord[::-1]:
            tl = tr = e
            for adj, cost in self.tree[v]:
                if self.par[v] == adj: continue
                lt[adj] = tl
                tl = op(tl, dp[adj], cost)
            for adj, cost in self.tree[v][::-1]:
                if self.par[v] == adj: continue
                rt[adj] = tr
                tr = op(tr, dp[adj], cost)
            dp[v] = tr
        for v in self.ord:
            if v == self.root: continue
            p = self.par[v]
            cost = self.cost[p]
            inv[v] = op(merge(lt[v], rt[v]), inv[p], cost)
            cost = self.cost[v]
            dp[v] = op(dp[v], inv[v], cost)
        return dp

import io, os
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline

MOD = 1000000007

N = int(input())

t = Tree(N)

for _ in range(N - 1):
    u, v, w = map(int, input().split())
    u -= 1; v -= 1
    t.add_edge(u, v, w)

e = (1, 0, 0)

def op(p, c, w):
    ps, pd, pds = p
    cs, cd, cds = c
    size = ps + cs
    dist = (pd + cd + w * cs) % MOD
    dsq = (pds + cds + w**2 * cs + 2 * w * cd) % MOD
    return size, dist, dsq

id = (0, 0, 0)

def merge(lt, rt):
    ls, ld, lds = lt
    rs, rd, rds = rt
    size = ls + rs - 1
    dist = (ld + rd) % MOD
    dsq = (lds + rds) % MOD
    return size, dist, dsq

dp = t.rerooting(op, e, merge, id)

res = 0

for size, dist, dsq in dp:
    res += dsq
    res %= MOD

print(res * pow(2, MOD - 2, MOD) % MOD)
0