SPOJ 375 Query on a tree

SPOJ_375

    树链剖分的处女作终于AC啦，O(∩_∩)O哈哈~

    思想是从这篇博客里面学来的：http://blog.sina.com.cn/s/blog_6974c8b20100zc61.html，上面讲得通俗易懂。只不过我在预处理的时候是用他说的避免暴栈的bfs方式来做的。

#include<stdio.h>
#include<string.h>
#define MAXD 10010
#define MAXM 20010
#define NINF 0xc3c3c3c3
int N, cnt, first[MAXD], e, next[MAXM], v[MAXM], fa[MAXD], dep[MAXD], size[MAXD], son[MAXD], top[MAXD], w[MAXD], max[4 * MAXD];
int q[MAXD];
struct Edge
{
    int x, y, z;
}edge[MAXD];
int Max(int x, int y)
{
    return x > y ? x : y;
}
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 prepare()
{
    int i, j, k, x, y, rear = 0;
    q[rear ++] = 1;
    dep[1] = 1, fa[1] = 0, son[1] = 0;
    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])
        {
            for(y = x; y != 0; y = son[y])
            {
                top[y] = x;
                w[y] = ++ cnt;
            }
        }
    }
}
void update(int cur)
{
    max[cur] = Max(max[cur << 1], max[cur << 1 | 1]);
}
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)
    {
        max[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));
    scanf("%d", &N);
    for(i = 1; i < N; i ++)
    {
        scanf("%d%d%d", &edge[i].x, &edge[i].y, &edge[i].z);
        add(edge[i].x, edge[i].y), add(edge[i].y, edge[i].x);
    }
    prepare();
    memset(max, 0xc3, sizeof(max));
    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 query(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 = Max(ans, max[cur]);
        return ;
    }
    if(mid >= s)
        query(ls, x, mid, s, t, ans);
    if(mid + 1 <= t)
        query(rs, mid + 1, y, s, t, ans);
}
void Query(int x, int y)
{
    int fx = top[x], fy = top[y], ans = NINF;
    while(fx != fy)
    {
        if(dep[fx] > dep[fy])
            Swap(fx, fy), Swap(x, y);
        query(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);
        query(1, 1, N, w[son[x]], w[y], ans);
    }
    printf("%d\n", ans);
}
void solve()
{
    int i, x, y;
    char op[10];
    for(;;)
    {
        scanf("%s", op);
        if(op[0] == 'D')
            break;
        scanf("%d%d", &x, &y);
        if(op[0] == 'C')
            refresh(1, 1, N, w[edge[x].y], y);
        else
            Query(x, y);
    }
}
int main()
{
    int t;
    scanf("%d", &t);
    while(t --)
    {
        init();
        solve();
    }
    return 0;
}