#include <bits/stdc++.h> using namespace std; const int N = 1000006; int gcd(int x, int y) { while (y) { x %= y; swap(x, y); } return x; } struct ban { int x, y; ban() { x = 0; y = 1; } ban(int x, int y) { int g = gcd(x, y); this->x = x / g; this->y = y / g; } }; bool operator<(const ban& a, const ban& b) { return (a.x * 1LL * b.y) < (b.x * 1LL * a.y); } int n; vector<int> a[N]; int u[N]; int q[N]; void dfs(int x, int p) { if (u[x] == 1) q[x] = 1; for (int i = 0; i < a[x].size(); ++i) { int h = a[x][i]; if (h == p) continue; dfs(h, x); if (u[x] == 1) q[x] = max(q[x], q[h] + 1); } } ban ans; void dfs1(int x, int p, int qp) { multiset<int> s; s.insert(qp); s.insert(0); for (int i = 0; i < a[x].size(); ++i) { int h = a[x][i]; if (h == p) continue; s.insert(q[h]); } ban t = ban(u[x], *(--s.end()) + 1 + *(--(--s.end()))); if (t < ans) ans = t; for (int i = 0; i < a[x].size(); ++i) { int h = a[x][i]; if (h == p) continue; s.erase(s.find(q[h])); if (u[x] == 1) dfs1(h, x, *(--s.end()) + 1); else dfs1(h, x, 0); s.insert(q[h]); } } int main() { scanf("%d", &n); for (int i = 0; i < n - 1; ++i) { int x, y; scanf("%d%d", &x, &y); a[x].push_back(y); a[y].push_back(x); } for (int i = 1; i <= n; ++i) scanf("%d", &u[i]); dfs(1, 1); ans = ban(u[1], 1); dfs1(1, 1, 0); printf("%d/%d\n", ans.x, ans.y); return 0; }

mag.cpp: In function 'void dfs(int, int)':
mag.cpp:43:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a[x].size(); ++i)
                     ~~^~~~~~~~~~~~~
mag.cpp: In function 'void dfs1(int, int, int)':
mag.cpp:61:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a[x].size(); ++i)
                     ~~^~~~~~~~~~~~~
mag.cpp:71:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a[x].size(); ++i)
                     ~~^~~~~~~~~~~~~
mag.cpp: In function 'int main()':
mag.cpp:87:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~
mag.cpp:91:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &x, &y);
         ~~~~~^~~~~~~~~~~~~~~~
mag.cpp:96:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &u[i]);
         ~~~~~^~~~~~~~~~~~~