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| #include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 5e5 + 10, M = 1e6 + 10;
int n, st;
LL ans, d[N];
int idx, hd[N], nxt[M], edg[M], wt[M];
void add(int a, int b, int c)
{
nxt[++idx] = hd[a];
hd[a] = idx;
edg[idx] = b;
wt[idx] = c;
}
void dfs(int x, int fa)
{
for (int i = hd[x]; ~i; i = nxt[i])
if (edg[i] != fa)
{
dfs(edg[i], x);
d[x] = max(d[x], d[edg[i]] + wt[i]);
}
for (int i = hd[x]; ~i; i = nxt[i])
if (edg[i] != fa)
ans += d[x] - (d[edg[i]] + wt[i]);
}
int main()
{
scanf("%d%d", &n, &st);
for (int i = 1; i <= n; i++)
hd[i] = -1;
for (int i = 1, a, b, c; i < n; i++)
{
scanf("%d%d%d", &a, &b, &c);
add(a, b, c);
add(b, a, c);
}
dfs(st, 0);
printf("%d", ans);
return 0;
}
|