Refactor: Quy nguyen bfs for his girlfriend

Người ta nói BFS là thuật toán có thể tìm dc mọi thứ trên thế giới
Dùng BFS nhưng  sao Quý ko tìm dc trái tym Nhi

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

Blue/Session 07 - DFS/Hackerearth_bishu-and-his-girlfriend.py

@@ -1,54 +1,42 @@
-#  Problem from Hackerearth
-#  https://www.hackerearth.com/fr/practice/algorithms/graphs/depth-first-search/practice-problems/algorithm/bishu-and-his-girlfriend/description/
+#  Quy Nguyen's late-night adventure.
 
+# https://www.hackerearth.com/fr/practice/algorithms/graphs/depth-first-search/practice-problems/algorithm/bishu-and-his-girlfriend/description/
+# Quy Nguyen lives in node 1, desperate and lonely
+# He must find the nearest "girlfriend" in the Geylang tree
+# (We all know who Quy Nguyen is really looking for)
+# If tie on distance, pick the one with smallest node number
 
-def find_girl(N, graph, girls):
-    s = []
-    visited = [False for i in range(N + 1)]
+from collections import deque
 
-    roads = [0 for i in range(N + 1)]
-
-    visited[1] = True
-    s.append(1)
-
-    selected_girl = N
-    selected_road = N
-
-    while len(s) > 0:
-        u = s[-1]
-        s.pop()
-
-        for v in graph[u]:
-            if not visited[v]:
-                roads[v] = roads[u] + 1
-                if roads[v] <= selected_road:
-                    if girls[v]:
-                        if roads[v] < selected_road or (roads[v] == selected_road and selected_girl > v):
-                            selected_girl = v
-                            selected_road = roads[v]
-                            visited[v] = True
-                    else:
-                        visited[v] = True
-                        s.append(v)
-
-    return selected_girl
-
-
-def solution():
+def solve():
     N = int(input())
-    roads = []
-    graph = [[] for i in range(N + 1)]
-    for i in range(N-1):
+    g = [[] for _ in range(N + 1)]
+    for _ in range(N - 1):
         u, v = map(int, input().split())
-        graph[u].append(v)
-        graph[v].append(u)
+        g[u].append(v)
+        g[v].append(u)
 
     Q = int(input())
-    girls = [0 for i in range(N + 1)]
-    for i in range(Q):
-        girls[int(input())] = 1
-
-    print(find_girl(N, graph, girls))
-
 
-solution()
+    # Mark the "ladies of the night" locations
+    hoes = set(int(input()) for _ in range(Q))
+
+    # BFS from Quy Nguyen's house (node 1) — the horny search algorithm
+    dist = [-1] * (N + 1)
+    dist[1] = 0
+    q = deque([1])
+    best, best_d = N, N  # worst case: the farthest hooker
+    while q:
+        u = q.popleft()
+        if u in hoes and (dist[u] < best_d or (dist[u] == best_d and u < best)):
+            best, best_d = u, dist[u]  # found a closer thot
+        for v in g[u]:
+            if dist[v] == -1:
+                dist[v] = dist[u] + 1
+                if dist[v] <= best_d:  # pruning: no point going deeper than current best
+                    q.append(v)
+
+    # Do we even have Jenny in the testcases? Wondering
+    print(best)
+
+solve()