結果

問題 No.1333 Squared Sum
ユーザー Kiri8128
提出日時 2021-01-08 22:54:05
言語 PyPy3
(7.3.15)
結果
AC  
実行時間 1,149 ms / 2,000 ms
コード長 1,580 bytes
コンパイル時間 335 ms
コンパイル使用メモリ 82,432 KB
実行使用メモリ 197,152 KB
最終ジャッジ日時 2024-11-16 14:37:13
合計ジャッジ時間 31,060 ms
ジャッジサーバーID
(参考情報)
judge5 / judge4
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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 #
プレゼンテーションモードにする

# DP
import sys
input = sys.stdin.readline
from collections import deque
mod = 10 ** 9 + 7
N = int(input())
X = [[] for i in range(N)]
for i in range(N-1):
x, y, w = map(int, input().split())
X[x-1].append((y-1, w))
X[y-1].append((x-1, w))
P = [-1] * N
Q = deque([0])
R = []
D = [0] * N
while Q:
i = deque.popleft(Q)
R.append(i)
for a, w in X[i]:
if a != P[i]:
P[a] = i
D[a] = w
X[a].remove((i, w))
deque.append(Q, a)
#
# a0 += b0
# a1 += b1 + b0 * d
# a2 += b0 * d ** 2 + 2 * b1 * d + b2
##### Settings
unit = (0, 0, 0)
merge = lambda a, b: ((a[0] + b[0]) % mod, (a[1] + b[1]) % mod, (a[2] + b[2]) % mod)
## ↓ 2
def adj_bu(a, i, p):
a0, a1, a2 = a
a0 += 1
d = D[i]
return (a0, (a1 + a0 * d) % mod, (a0 * d ** 2 + 2 * a1 * d + a2) % mod)
def adj_td(a, i, p):
a0, a1, a2 = a
a0 += 1
d = D[i]
return (a0, (a1 + a0 * d) % mod, (a0 * d ** 2 + 2 * a1 * d + a2) % mod)
adj_fin = lambda a, i: a[2]
#####
ME = [unit] * N
XX = [0] * N
TD = [unit] * N
for i in R[1:][::-1]:
p = P[i]
XX[i] = adj_bu(ME[i], i, p)
ME[p] = merge(ME[p], XX[i])
XX[R[0]] = adj_fin(ME[R[0]], R[0])
for i in R:
ac = TD[i]
for j, _ in X[i]:
TD[j] = ac
ac = merge(ac, XX[j])
ac = unit
for j, _ in X[i][::-1]:
TD[j] = adj_td(merge(TD[j], ac), j, i)
ac = merge(ac, XX[j])
XX[j] = adj_fin(merge(ME[j], TD[j]), j)
print(sum(XX) * (mod + 1) // 2 % mod)
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