結果

問題 No.2337 Equidistant
コンテスト
ユーザー LyricalMaestro
提出日時 2026-01-18 00:42:13
言語 PyPy3
(7.3.17)
結果
AC  
実行時間 2,497 ms / 4,000 ms
コード長 4,160 bytes
記録
記録タグの例:
初AC ショートコード 純ショートコード 純主流ショートコード 最速実行時間
コンパイル時間 352 ms
コンパイル使用メモリ 82,872 KB
実行使用メモリ 243,440 KB
最終ジャッジ日時 2026-01-18 00:42:50
合計ジャッジ時間 35,589 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge1
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 1
other AC * 28
権限があれば一括ダウンロードができます

ソースコード

diff #
raw source code 

## https://yukicoder.me/problems/no/2337

from collections import deque

def calcurate_next_childs(N, next_nodes):
    parents = [-2] * N
    parents[0] = -1
    total_childs = [0] * N
    next_childs = [{} for _ in range(N)]

    stack= deque()
    stack.append((0, 0))
    while len(stack) > 0:
        v, index = stack.pop()

        while index < len(next_nodes[v]):
            w = next_nodes[v][index]
            if w == parents[v]:
                index += 1
                continue

            parents[w] = v
            stack.append((v, index + 1))
            stack.append((w, 0))
            break

        if index == len(next_nodes[v]):
            p = parents[v]
            if p != -1:
                total_childs[p] += 1 + total_childs[v]
                next_childs[p][v] = 1 + total_childs[v]
    
    queue = deque()
    queue.append((0, -1, 0))
    depth = [0] * N
    while len(queue) > 0:
        v, c, d = queue.popleft()
        depth[v] = d
        if parents[v] != -1:
            p = parents[v]
            total_childs[v] += 1 + c
            next_childs[v][p] = 1 + c
            
        for w in next_nodes[v]:
            if parents[v] == w:
                continue

            c = total_childs[v] - next_childs[v][w]
            queue.append((w, c, d + 1))
    return next_childs, parents, depth
            

def main():
    N, Q = map(int, input().split())
    next_nodes = [[] for _ in range(N)]
    for _ in range(N - 1):
        u, v = map(int, input().split())
        next_nodes[u - 1].append(v - 1)
        next_nodes[v - 1].append(u - 1)

    st = []
    for _ in range(Q):
        s, t = map(int, input().split())
        st.append((s -1 ,t - 1))
    
    # 全方位木dp
    next_childs, parents, depth = calcurate_next_childs(N, next_nodes)

    # ダブリング
    k = 0
    while (1 << k) < N:
        k += 1
    max_k = k

    parents_list = [[-1] * N for _ in range(max_k + 1)]
    parents_list[0] = parents
    for k in range(1, max_k + 1):
        for i in range(N):
            p = parents_list[k - 1][i]
            if p != -1:
                parents_list[k][i] = parents_list[k - 1][p]

    def calc_lca(s, t):
        # depth[s] > depth[v]にしたい
        if depth[s] < depth[t]:
            t, s = s, t

        if depth[s] > depth[t]:
            d = depth[s] - depth[t]
            for k in reversed(range(max_k + 1)):
                if d >= (1 << k):
                    s = parents_list[k][s]
                    d -= (1 << k)
        
        if s == t:
            return s
        else:
            d = depth[s]
            for k in reversed(range(max_k + 1)):
                if d >= (1 << k):
                    ps = parents_list[k][s]
                    pt = parents_list[k][t]
                    if ps != pt:
                        s = ps
                        t = pt
                        d -= (1 << k)
            return parents_list[0][s]
        
    def calc_p(s, d):
        for k in reversed(range(max_k + 1)):
            if d >= (1 << k):
                s = parents_list[k][s]
                d -= (1 << k)
        return s

    # 本回答
    for s, t in st:
        lca_v = calc_lca(s, t)

        dist = depth[s] + depth[t] - 2 * depth[lca_v]
        if dist % 2 != 0:
            print(0)
        else:
            dist_half = dist // 2
            if dist_half == depth[s] - depth[lca_v]:
                s1 = calc_p(s, dist_half - 1)
                t1 = calc_p(t, dist_half - 1)
                ans = N - next_childs[lca_v][s1] - next_childs[lca_v][t1]
                print(ans)
            else:
                if depth[s] < depth[t]:
                    p = calc_p(t, dist_half)
                    p1 = calc_p(t, dist_half - 1)
                    p2 = parents[p]
                    ans = N - next_childs[p][p1] - next_childs[p][p2]
                else:
                    p = calc_p(s, dist_half)
                    p1 = calc_p(s, dist_half - 1)
                    p2 = parents[p]
                    ans = N - next_childs[p][p1] - next_childs[p][p2]

                print(ans)

                







if __name__ == "__main__":
    main()
0