URAL 1471 Tree

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;
}