URAL_1471
这个题目可以用树链剖分做,另外推荐一个讲树链剖分通俗易懂的博客:http://blog.sina.com.cn/s/blog_6974c8b20100zc61.html。
#include<stdio.h>
#include<string.h>
#define MAXD 50010
#define MAXM 100010
int N, Q, first[MAXD], next[MAXM], v[MAXM], e;
int fa[MAXD], dep[MAXD], son[MAXD], size[MAXD], w[MAXD], top[MAXD], cnt;
int q[MAXD], sum[4 * MAXD];
struct Edge
{
int x, y, z;
}edge[MAXD];
void Swap(int &x, int &y)
{
int t;
t = x, x = y, y = t;
}
void add(int x, int y)
{
v[e] = y;
next[e] = first[x], first[x] = e ++;
}
void update(int cur)
{
sum[cur] = sum[cur << 1] + sum[cur << 1 | 1];
}
void prepare()
{
int i, j, x, rear = 0;
fa[1] = 0, dep[1] = 1;
q[rear ++] = 1;
for(i = 0; i < rear; i ++)
{
x = q[i];
for(j = first[x]; j != -1; j = next[j])
if(v[j] != fa[x])
{
fa[v[j]] = x, dep[v[j]] = dep[x] + 1;
q[rear ++] = v[j];
}
}
size[0] = 0;
for(i = rear - 1; i >= 0; i --)
{
x = q[i];
size[x] = 1, son[x] = 0;
for(j = first[x]; j != -1; j = next[j])
if(v[j] != fa[x])
{
size[x] += size[v[j]];
if(size[v[j]] > size[son[x]])
son[x] = v[j];
}
}
cnt = 0;
memset(top, 0, sizeof(top));
for(i = 0; i < rear; i ++)
{
x = q[i];
if(top[x] == 0)
{
for(j = x; j != 0; j = son[j])
top[j] = x, w[j] = ++ cnt;
}
}
}
void refresh(int cur, int x, int y, int k, int v)
{
int mid = (x + y) >> 1, ls = cur << 1, rs = cur << 1 | 1;
if(x == y)
{
sum[cur] = v;
return ;
}
if(k <= mid)
refresh(ls, x, mid, k, v);
else
refresh(rs, mid + 1, y, k, v);
update(cur);
}
void init()
{
int i, x, y, z;
e = 0;
memset(first, -1, sizeof(first));
for(i = 1; i < N; i ++)
{
scanf("%d%d%d", &x, &y, &z);
++ x, ++ y;
edge[i].x = x, edge[i].y = y, edge[i].z = z;
add(x, y), add(y, x);
}
prepare();
memset(sum, 0, sizeof(sum));
for(i = 1; i < N; i ++)
{
if(dep[edge[i].x] > dep[edge[i].y])
Swap(edge[i].x, edge[i].y);
refresh(1, 1, N, w[edge[i].y], edge[i].z);
}
}
void Search(int cur, int x, int y, int s, int t, int &ans)
{
int mid = (x + y) >> 1, ls = cur << 1, rs = cur << 1 | 1;
if(x >= s && y <= t)
{
ans += sum[cur];
return ;
}
if(mid >= s)
Search(ls, x, mid, s, t, ans);
if(mid + 1 <= t)
Search(rs, mid + 1, y, s, t, ans);
}
void deal(int x, int y)
{
int fx = top[x], fy = top[y], ans = 0;
while(fx != fy)
{
if(dep[fx] > dep[fy])
Swap(fx, fy), Swap(x, y);
Search(1, 1, N, w[fy], w[y], ans);
y = fa[fy], fy = top[y];
}
if(x != y)
{
if(dep[x] > dep[y])
Swap(x, y);
Search(1, 1, N, w[son[x]], w[y], ans);
}
printf("%d\n", ans);
}
void solve()
{
int i, q, x, y;
scanf("%d", &q);
for(i = 0; i < q; i ++)
{
scanf("%d%d", &x, &y);
deal(x + 1, y + 1);
}
}
int main()
{
while(scanf("%d", &N) == 1)
{
init();
solve();
}
return 0;
}