This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#define eb emplace_back
#define INFLL (0x3f3f3f3f3f3f3f3fll)
using namespace std;
typedef long long ll;
const int MAXN = 200055;
ll D[MAXN*2], E[MAXN*2];
ll MX[MAXN][2];
ll S[MAXN];
int O[MAXN*2];
bitset<MAXN*2> chk;
vector<int> G[MAXN];
int cnt[MAXN];
int A[MAXN], B[MAXN], C[MAXN];
ll Ans;
int N;
int getC(int e) { return (e&1) ? N-cnt[B[e>>1]] : cnt[B[e>>1]]; }
void dfs(int i) {
cnt[i] = 1;
for(int e : G[i]) {
int v = A[e]^B[e]^i;
if(cnt[v]) continue;
dfs(v);
cnt[i] += cnt[v];
}
}
int main() {
ios::sync_with_stdio(false);
cin >> N;
for(int i = 0; i < N-1; i++) {
cin >> A[i] >> B[i] >> C[i];
G[A[i]].eb(i);
G[B[i]].eb(i);
}
dfs(1);
for(int i = 0; i < N-1; i++)
if(cnt[A[i]] < cnt[B[i]]) swap(A[i], B[i]);
fill(MX[0], MX[N]+2, -INFLL);
iota(O, O+(N-1)*2, 0); sort(O, O+(N-1)*2, [&](int a, int b) {
return getC(a) < getC(b);
});
for(int oi = 0, e, v, p; oi < (N-1)*2; oi++) {
e = O[oi]; v = B[e>>1]; p = A[e>>1];
if(e&1) swap(v, p);
chk[e] = true;
D[e] = S[v] - (chk[e^1] ? max(D[e^1], E[e^1]) : 0);
if(chk[e^1]) {
ll t = -max(D[e^1], E[e^1]) + D[e^1] + C[e>>1];
E[e] = MX[v][0] == t ? MX[v][1] : MX[v][0];
} else E[e] = MX[v][0];
E[e] += D[e] + C[e>>1];
S[p] += max(D[e], E[e]);
{
ll t = -max(D[e], E[e]) + D[e] + C[e>>1];
if(MX[p][0] < t) swap(MX[p][0], t);
if(MX[p][1] < t) swap(MX[p][1], t);
}
}
for(int i = 1; i <= N; i++) {
ll sum = 0;
for(int e : G[i]) {
int v = A[e]^B[e]^i;
e = (e<<1) | (B[e] == i ? 1 : 0);
sum += max(D[e], E[e]);
}
if(Ans < sum) Ans = sum;
}
cout << Ans << endl;
return 0;
}
Compilation message (stderr)
beads.cpp: In function 'int main()':
beads.cpp:76:8: warning: unused variable 'v' [-Wunused-variable]
int v = A[e]^B[e]^i;
^
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