[2025-04-08] sungchan #456

BaekJoon/11438/sungchan.py

@@ -0,0 +1,58 @@
+import sys
+from collections import deque
+input = sys.stdin.readline
+
+n = int(input())
+LOG = 21 # 100,000 기준으로 log(100,000)
+
+
+graph = [[] for _ in range(n+1)]
+for _ in range(n-1):
+    a, b = map(int, input().split())
+    graph[a].append(b)
+    graph[b].append(a)
+
+depth = [0] * (n+1)
+parent = [[0] * (n+1) for _ in range(LOG)]
+
+def bfs(root):
+    queue = deque([root])
+    visited = [False] * (n + 1)
+    visited[root] = True
+    while queue:
+        node = queue.popleft()
+        for next_node in graph[node]:
+            if not visited[next_node]:
+                visited[next_node] = True
+                depth[next_node] = depth[node] + 1
+                parent[0][next_node] = node
+                queue.append(next_node)
+
+bfs(1)  # 루트는 1번 노드로 가정
+
+for k in range(1, LOG):
+    for v in range(1, n + 1):
+        parent[k][v] = parent[k - 1][parent[k - 1][v]]
+
+def lca(u, v):
+    if depth[u] < depth[v]:
+        u, v = v, u
+
+    for k in reversed(range(LOG)):
+        if depth[u] - depth[v] >= (1 << k):
+            u = parent[k][u]
+
+    if u == v:
+        return u
+
+    for k in reversed(range(LOG)):
+        if parent[k][u] != parent[k][v]:
+            u = parent[k][u]
+            v = parent[k][v]
+
+    return parent[0][u]
+
+M = int(input())
+for _ in range(M):
+    u, v = map(int, input().split())
+    print(lca(u, v))