#1059534 (PyPy3) No.1976 Cut then Connect

• 問題: No.1976 Cut then Connect
• ユーザー: lam6er
• 提出日時: 2025-03-26 15:50:01
• 言語: PyPy3 (7.3.15)
• 結果: WA
• 実行時間: -
• コード長: 6,599 bytes
• コンパイル時間: 248 ms
• コンパイル使用メモリ: 82,456 KB
• 実行使用メモリ: 157,012 KB
• 最終ジャッジ日時: 2025-03-26 15:50:28
• 合計ジャッジ時間: 13,311 ms
• ジャッジサーバーID （参考情報）: judge2 / judge1

ファイルパターン	結果
sample	AC * 2
other	AC * 8 WA * 23

ソースコード

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import sys
from sys import stdin
from collections import deque
sys.setrecursionlimit(1 << 25)
def main():
    N = int(stdin.readline())
    edges = [[] for _ in range(N+1)]
    for _ in range(N-1):
        u, v = map(int, stdin.readline().split())
        edges[u].append(v)
        edges[v].append(u)
    
    root = 1
    parent = [0]*(N+1)
    children = [[] for _ in range(N+1)]
    visited = [False]*(N+1)
    q = deque([root])
    visited[root] = True
    while q:
        u = q.popleft()
        for v in edges[u]:
            if not visited[v]:
                visited[v] = True
                parent[v] = u
                children[u].append(v)
                q.append(v)
    
    down_diameter = [0]*(N+1)
    max_depth = [0]*(N+1)
    
    post_order = []
    stack = [(root, False)]
    while stack:
        u, processed = stack.pop()
        if processed:
            post_order.append(u)
            max_d = 0
            max1 = -1
            max2 = -1
            diam = 0
            for v in children[u]:
                current_depth = max_depth[v] + 1
                if current_depth > max1:
                    max2 = max1
                    max1 = current_depth
                elif current_depth > max2:
                    max2 = current_depth
                if down_diameter[v] > diam:
                    diam = down_diameter[v]
            if max1 + max2 > diam:
                diam = max1 + max2
            down_diameter[u] = diam
            max_depth[u] = max1 if max1 != -1 else 0
        else:
            stack.append((u, True))
            for v in reversed(children[u]):
                stack.append((v, False))
    
    up_diameter = [0]*(N+1)
    up_depth = [0]*(N+1)
    
    pre_order = deque()
    pre_order.append(root)
    q = deque([root])
    while q:
        u = q.popleft()
        for v in children[u]:
            pre_order.append(v)
            q.append(v)
    
    prefix_max_depth = {}
    prefix_second_max_depth = {}
    prefix_max_down = {}
    suffix_max_depth = {}
    suffix_second_max_depth = {}
    suffix_max_down = {}
    
    for u in pre_order:
        child_list = children[u]
        k = len(child_list)
        if k == 0:
            continue
        
        prefix_max_depth[u] = [ -1 ] * (k+1)
        prefix_second_max_depth[u] = [ -1 ] * (k+1)
        prefix_max_down[u] = [ -1 ] * (k+1)
        current_max_depth = -1
        current_second_max_depth = -1
        current_max_down = -1
        
        for i in range(1, k+1):
            v = child_list[i-1]
            depth = max_depth[v] + 1
            down = down_diameter[v]
            if depth > current_max_depth:
                current_second_max_depth = current_max_depth
                current_max_depth = depth
            elif depth > current_second_max_depth:
                current_second_max_depth = depth
            if down > current_max_down:
                current_max_down = down
            prefix_max_depth[u][i] = current_max_depth
            prefix_second_max_depth[u][i] = current_second_max_depth
            prefix_max_down[u][i] = current_max_down
        
        suffix_max_depth[u] = [ -1 ] * (k+1)
        suffix_second_max_depth[u] = [ -1 ] * (k+1)
        suffix_max_down[u] = [ -1 ] * (k+1)
        current_max_depth = -1
        current_second_max_depth = -1
        current_max_down = -1
        
        for i in range(k-1, -1, -1):
            v = child_list[i]
            depth = max_depth[v] + 1
            down = down_diameter[v]
            if depth > current_max_depth:
                current_second_max_depth = current_max_depth
                current_max_depth = depth
            elif depth > current_second_max_depth:
                current_second_max_depth = depth
            if down > current_max_down:
                current_max_down = down
            suffix_max_depth[u][i] = current_max_depth
            suffix_second_max_depth[u][i] = current_second_max_depth
            suffix_max_down[u][i] = current_max_down
        
        for i in range(k):
            v = child_list[i]
            if k == 1:
                max_other_depth = -1
                second_other_depth = -1
                max_down_other = -1
            else:
                max_prefix = prefix_max_depth[u][i] if i > 0 else -1
                max_suffix = suffix_max_depth[u][i+1] if i+1 < k else -1
                max_other_depth = max(max_prefix, max_suffix)
                down_prefix = prefix_max_down[u][i] if i > 0 else -1
                down_suffix = suffix_max_down[u][i+1] if i+1 < k else -1
                max_down_other = max(down_prefix, down_suffix)
                if max_prefix == -1 and max_suffix == -1:
                    max_other_depth = -1
                    second_other_depth = -1
                elif max_prefix > max_suffix:
                    second_prefix = prefix_second_max_depth[u][i] if i > 0 else -1
                    second_other_depth = max(second_prefix, max_suffix)
                elif max_prefix < max_suffix:
                    second_suffix = suffix_second_max_depth[u][i+1] if i+1 < k else -1
                    second_other_depth = max(max_prefix, second_suffix)
                else:
                    second_prefix = prefix_second_max_depth[u][i] if i > 0 else -1
                    second_suffix = suffix_second_max_depth[u][i+1] if i+1 < k else -1
                    second_other_depth = max(second_prefix, second_suffix)
            
            a = up_diameter[u]
            b = max_down_other if max_down_other != -1 else 0
            c = (up_depth[u] + max_other_depth + 1) if max_other_depth != -1 else 0
            if max_other_depth == -1:
                c = up_depth[u] + 1
            d = (max_other_depth + second_other_depth + 2) if (max_other_depth != -1 and second_other_depth != -1) else 0
            current_diam = max(a, b, c, d)
            up_diameter[v] = current_diam
            
            if max_other_depth == -1:
                up_depth_v = up_depth[u] + 1
            else:
                up_depth_v = max(up_depth[u] + 1, max_other_depth + 1)
            up_depth[v] = up_depth_v
    
    min_diam = float('inf')
    for u in range(1, N+1):
        for v in children[u]:
            d1 = down_diameter[v]
            d2 = up_diameter[v]
            r1 = (d1 + 1) // 2
            r2 = (d2 + 1) // 2
            candidate = max(d1, d2, r1 + r2 + 1)
            if candidate < min_diam:
                min_diam = candidate
    if N == 2:
        print(1)
    else:
        print(min_diam)
if __name__ == "__main__":
    main()
 
 
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