結果

問題 No.1976 Cut then Connect
コンテスト
ユーザー tamato
提出日時 2022-06-10 23:33:08
言語 PyPy3
(7.3.15)
結果
RE  
実行時間 -
コード長 3,400 bytes
コンパイル時間 148 ms
コンパイル使用メモリ 82,176 KB
実行使用メモリ 132,628 KB
最終ジャッジ日時 2024-09-21 06:59:26
合計ジャッジ時間 6,821 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge2
このコードへのチャレンジ
（要ログイン）
ファイルパターン 結果
sample AC * 1 RE * 1
other AC * 11 WA * 7 RE * 13
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 # 

mod = 998244353


def main():
    import sys
    from collections import deque
    input = sys.stdin.readline

    def radius(v0, v1):
        que = deque()
        que.append(v0)
        seen = {}
        seen[v0] = 0
        v_last = 0
        while que:
            v = que.popleft()
            for u in adj[v]:
                if u == v1:
                    continue
                if u not in seen:
                    seen[u] = seen[v] + 1
                    que.append(u)
            v_last = v
        v0 = v_last
        que = deque()
        que.append(v0)
        seen = {}
        seen[v0] = 0
        v_last = 0
        while que:
            v = que.popleft()
            for u in adj[v]:
                if u == v1:
                    continue
                if u not in seen:
                    seen[u] = seen[v] + 1
                    que.append(u)
            v_last = v
        return seen[v_last]

    N = int(input())
    adj = [[] for _ in range(N + 1)]
    for _ in range(N - 1):
        a, b = map(int, input().split())
        adj[a].append(b)
        adj[b].append(a)

    que = deque()
    que.append(1)
    seen = [-1] * (N+1)
    seen[1] = 0
    par = [0] * (N+1)
    child = [[] for _ in range(N+1)]
    seq = []
    while que:
        v = que.popleft()
        seq.append(v)
        for u in adj[v]:
            if seen[u] == -1:
                seen[u] = seen[v] + 1
                par[u] = v
                child[v].append(u)
                que.append(u)
    seq.reverse()

    v0 = seq[0]
    que = deque()
    que.append(v0)
    seen = [-1] * (N+1)
    seen[v0] = 0
    par = [0] * (N+1)
    child = [[] for _ in range(N+1)]
    seq = []
    while que:
        v = que.popleft()
        seq.append(v)
        for u in adj[v]:
            if seen[u] == -1:
                seen[u] = seen[v] + 1
                par[u] = v
                child[v].append(u)
                que.append(u)
    seq.reverse()

    v1 = seq[0]
    D = seen[v1]
    if D & 1:
        v = v1
        for _ in range(D // 2):
            v = par[v]
        vl = v
        vr = par[v]

        dl = radius(vl, vr)
        dr = radius(vr, vl)

        print(max((dl + 1) // 2 + (dr + 1) // 2 + 1, dl, dr))
        assert False
    else:
        v = v1
        for _ in range(D // 2):
            v = par[v]
        v0 = v
        que = deque()
        que.append(v0)
        seen = [-1] * (N+1)
        seen[v0] = 0
        par = [0] * (N+1)
        child = [[] for _ in range(N+1)]
        seq = []
        while que:
            v = que.popleft()
            seq.append(v)
            for u in adj[v]:
                if seen[u] == -1:
                    seen[u] = seen[v] + 1
                    par[u] = v
                    child[v].append(u)
                    que.append(u)
        seq.reverse()

        subtree_len = [(0, 0)]
        for c in child[v0]:
            que = deque()
            seq = []
            que.append(c)
            while que:
                v = que.popleft()
                for vv in child[v]:
                    que.append(vv)
                seq.append(v)
            subtree_len.append((seen[seq[-1]], c))
        subtree_len.sort(key=lambda x: x[0], reverse=True)

        d1, d2, d3 = subtree_len[0][0], subtree_len[1][0], subtree_len[2][0]
        print(max(((d1 + d2) * 2 - 1) // 3 + 1, d2 + d3))


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