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| #pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define inline inline __attribute__((always_inline)) __attribute__((optimize("O3")))
const int iol = 1024 * 1024;
char buf[iol], *s1, *t, ioc;
bool iosig;
inline char read() {
if (s1 == t) {
t = (s1 = buf) + fread(buf, 1, iol, stdin);
if (s1 == t) return -1;
}
return *s1++;
}
template<class T>
inline bool read(T& x) {
iosig = false;
for (ioc = read(); !isdigit(ioc); ioc = read()) {
if (ioc == -1) return false;
if (ioc == '-') iosig = true;
}
x = 0;
while (ioc == '0') ioc = read();
for (; isdigit(ioc); ioc = read())
x = (x << 1) + (x << 3) + (ioc ^ '0');
s1--;
if (iosig) x = -x;
return true;
}
const int MAX_N = 300000 + 3, MAX_M = 300000 + 3, INF = 0x3f3f3f3f;
struct Node {
int v, w;
Node() {}
Node(int v1, int w1) : v(v1), w(w1) {}
};
vector<Node> pool[MAX_N * 2];
int n, m;
int queryFrom[MAX_M], queryTo[MAX_M], queryCost[MAX_M], queryLca[MAX_M];
int depth[MAX_N], dis[MAX_N], fc[MAX_N], ancestor[20][MAX_N];
int dfsSeq[MAX_N], cnt = 0;
inline void dfs() {
stack<int> st;
static bool vis[MAX_N];
memset(vis, 0, sizeof (bool) * n);
st.push(0);
ancestor[0][0] = -1, depth[0] = 0, dis[0] = 0;
while (!st.empty()) {
register int u = st.top();
if (!vis[u]) {
for (register int i = 0; i < pool[u].size(); i++) {
Node *e = &pool[u][i];
if (e->v != ancestor[0][u]) {
depth[e->v] = depth[u] + 1;
dis[e->v] = dis[u] + e->w;
fc[e->v] = e->w;
ancestor[0][e->v] = u;
st.push(e->v);
}
}
vis[u] = true;
} else dfsSeq[cnt++] = st.top(), st.pop();
}
}
inline int lca(int a, int b) {
if (depth[a] < depth[b]) swap(a, b);
register int bits = 0, q = 1;
while (depth[a] - q > 0) bits++, q <<= 1;
for (int i = bits; i >= 0; --i)
if (depth[a] - (1 << i) >= depth[b])
a = ancestor[i][a];
if (a == b) return a;
for (register int i = bits; i >= 0; --i)
if ((depth[a] - (1 << i) >= 0) && ancestor[i][a] != ancestor[i][b])
a = ancestor[i][a], b = ancestor[i][b];
return ancestor[0][a];
}
inline void init() {
dfs();
for (int w = 1; (1 << w) < n; ++w)
for (int i = 0; i < n; ++i)
if (depth[i] - (1 << w) >= 0)
ancestor[w][i] = ancestor[w - 1][ancestor[w - 1][i]];
for (int i = 0; i < m; ++i) {
int LCA = lca(queryFrom[i], queryTo[i]);
queryCost[i] = dis[queryFrom[i]] + dis[queryTo[i]] - 2 * dis[LCA];
queryLca[i] = LCA;
}
}
int s[MAX_N];
inline bool check(int t) {
int total = 0, maxT = 0;
memset(s, 0, sizeof (int) * n);
for (int i = 0; i < m; ++i) {
if (queryCost[i] <= t) continue;
total++;
s[queryFrom[i]]++, s[queryTo[i]]++, s[queryLca[i]] -= 2;
maxT = max(maxT, queryCost[i] - t);
}
for (int i = 0, u; i < n; ++i) {
u = dfsSeq[i];
s[ancestor[0][u]] += s[u];
}
int dec = 0;
for (int i = 0; i < n; ++i)
if (s[i] == total) dec = max(dec, fc[i]);
return maxT <= dec;
}
inline void solve() {
int l = -1, r = 300000000;
while (r - l > 1) {
int mid = (l + r) >> 1;
if (check(mid)) r = mid;
else l = mid;
}
cout << r << "\n";
}
int main() {
#ifndef ONLINE_JUDGE
freopen("in.in", "r", stdin);
#endif
read(n), read(m);
for (register int i = 0, f, t, c; i < n - 1; ++i) {
read(f), f--, read(t), t--, read(c);
pool[f].push_back(Node(t, c));
pool[t].push_back(Node(f, c));
}
for (register int i = 0; i < m; i++)
read(queryFrom[i]), queryFrom[i]--, read(queryTo[i]), queryTo[i]--;
init();
solve();
return 0;
}
|
