diff --git a/ZOJ/3937_csdn.cpp b/ZOJ/3937_csdn.cpp
new file mode 100644
index 0000000..5599d4e
--- /dev/null
+++ b/ZOJ/3937_csdn.cpp
@@ -0,0 +1,98 @@
+#include <bits/stdc++.h>
+using namespace std;
+typedef long long LL;
+
+class Solution {
+  static const int MAXN = 100000 + 10;
+  static const LL inf = 1ll << 60;
+  vector<int> G[MAXN];
+  int w[MAXN], n;
+
+  struct Line {// m * x + b
+    LL m, b;
+    double inter(const Line &r) const {
+      return (r.b - b) / (m - r.m);
+    }
+    inline LL eval(LL x) {return m * x + b;}
+  } Q[MAXN];a
+
+  int rt, mins, total, top;
+  int vs[MAXN], sz[MAXN], dep[MAXN];
+  LL val[MAXN], ps[MAXN], ret;
+
+  void getCenter(int u, int f = -1) {
+    int mx = 0; sz[u] = 1;
+    for (auto &v: G[u]) if (v != f && !vs[v]) {
+      getCenter(v, u); sz[u] += sz[v];
+      mx = max(mx, sz[v]);
+    }
+    mx = max(mx, total - sz[u]);
+    if (mx < mins) mins = mx, rt = u;
+  }
+  int dfs1(int u, int d = 1) {
+    ret = max(ret, val[d]);
+    for (auto &v: G[u]) if (!vs[v] && u > v) {
+      ps[v] = ps[u] + w[v];
+      val[d + 1] = val[d] + ps[v];
+      return dfs1(v, d + 1) + 1;
+    }
+    return 1;
+  }
+  void dfs2(int u, int d = 0, LL sum = 0) {
+    sum += 1ll * d * w[u];
+    // max(ps[u] * m + b + sum)
+    int left = 0, right = top - 2;
+    while (left < right) {
+      int mid = (left + right) >> 1;
+      if (Q[mid].eval(ps[u]) >= Q[mid + 1].eval(ps[u])) right = mid;
+      else left = mid + 1;
+    }
+    ret = max(ret, Q[left].eval(ps[u]) + sum);
+    if (left + 1 < top) ret = max(ret, Q[left + 1].eval(ps[u]) + sum);
+    for (auto &v: G[u]) if (!vs[v] && u < v) {
+      ps[v] = ps[u] + w[v];
+      dfs2(v, d + 1, sum);
+    }
+  }
+  void solve(int u, int _tot) {
+    total = _tot; mins = _tot * 2;
+    getCenter(u); u = rt; vs[u] = 1; getCenter(u);
+    val[1] = ps[u] = w[u];
+    int md = dfs1(u);
+    top = 0;
+    for (int i = 1; i <= md; ++i) {
+      Line now = (Line){i, val[i]};
+      while (top >= 2 && Q[top - 2].inter(Q[top - 1]) >= Q[top - 1].inter(now)) --top;
+      Q[top++] = now;
+    }
+    ps[u] = 0; dfs2(u);
+    for (int i = 0; i <= md; ++i) val[i] = -inf;
+    for (auto &v: G[u]) if (!vs[v]) {
+      solve(v, sz[v]);
+    }
+  }
+
+public:
+  void run() {
+    scanf("%d", &n);
+    for (int i = 0; i < n; ++i) {
+      scanf("%d", w + i); G[i].clear();
+    }
+    for (int i = 1; i < n; ++i) {
+      int x; scanf("%d", &x); --x;
+      G[x].push_back(i);
+      G[i].push_back(x);
+    }
+    ret = 0;
+    for (int i = 0; i < n; ++i) val[i] = -inf;
+    memset(vs, 0, sizeof(vs[0]) * n);
+    solve(0, n);
+    printf("%lld\n", ret);
+  }
+} sol;
+
+int main() {
+  int T; scanf("%d", &T);
+  for (int cas = 1; cas <= T; ++cas) sol.run();
+  return 0;
+}