SPOJ QTREE-Query on a tree-树链剖分-边权

用每个点代表父节点到此点的边。建立一一映射后就可以用点权的方法处理了。

注意的是路径两端节点的处理

#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

const int maxn = 1e5+5;
int val[maxn],dep[maxn],siz[maxn],top[maxn],id[maxn],son[maxn],fa[maxn];
int topw,M;

vector<int> G[maxn];
struct Edge{
    int x,y,val;
}e[maxn];

void dfs_1(int u,int f,int d)
{
    fa[u] = f;
    son[u] = 0;
    siz[u] = 1;
    dep[u] = d;

    for(int i=0;i<G[u].size();i++) if(G[u][i] != f )
    {
        dfs_1(G[u][i],u,d+1);
        siz[u] += siz[G[u][i]];
        if(siz[son[u] ] < siz[G[u][i] ])
        {
            son[u] = G[u][i];
        }
    }
}

void dfs_2(int u,int tp)
{
    top[u] = tp;
    id[u] = ++topw;
    if(son[u]) dfs_2(son[u],tp);
    for(int i=0;i<G[u].size();i++) if(G[u][i] != fa[u] && G[u][i] != son[u])
    {
        dfs_2(G[u][i],G[u][i]);
    }
}

int N,T;

void debug()
{
    for(int i=1;i<=N;i++)
    {
        printf("%d siz:%d son:%d dep:%d fa:%d ",i,siz[i],son[i],dep[i],fa[i]);
        printf("top:%d id:%d
",top[i],id[i]);
    }
}

/*-------------------------------------*/
//segment Tree
#define lson(x) (x<<1)
#define rson(x) (x<<1|1)

struct SegmentTree{
    int l,r,val;
}sgtree[4*maxn];

void pushup(int x)
{
    sgtree[x].val = max(sgtree[lson(x)].val,sgtree[rson(x)].val);
}

void Build(int l,int r,int x)
{
    sgtree[x].l = l;
    sgtree[x].r = r;
    if(l==r)
    {
        sgtree[x].val = val[l];
        return ;
    }
    int mid = (l+r)>>1;
    Build(l,mid,lson(x));
    Build(mid+1,r,rson(x));
    pushup(x);
}

void update(int x,int v,int add)
{
    if(sgtree[x].l == sgtree[x].r)
    {
        sgtree[x].val = add;
        //printf("change:%d %d
",v,sgtree[x].l);
        return ;
    }
    int mid = (sgtree[x].l+sgtree[x].r)>>1;
    if(v <= mid) update(lson(x),v,add);
    else         update(rson(x),v,add);
    pushup(x);
}

int query(int x,int l,int r)
{
    if(sgtree[x].l >= l && sgtree[x].r <= r)
    {
        return sgtree[x].val;
    }
    int mid = (sgtree[x].l+sgtree[x].r)>>1;
    int ans = 0;
    if(l <= mid) ans = max(ans,query(lson(x),l,r));
    if(r >  mid) ans = max(ans,query(rson(x),l,r));
    return ans;
}

int Find(int u,int v)
{
    int ans = 0,fu = top[u],fv = top[v];
    while(fu != fv)
    {
        if(dep[fu] < dep[fv])
        {
            swap(fu,fv);swap(u,v);
        }
        ans = max(ans,query(1,id[fu],id[u]));
        u = fa[fu];
        fu = top[u];
    }
    if(u == v) return ans;
    if(dep[u]>dep[v]) swap(u,v);
    return max(ans,query(1,id[son[u] ],id[v]));
}

int main()
{
    //freopen("input.in","r",stdin);
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&N);
        for(int i=1,a,b,c;i<N;i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            e[i].x = a;
            e[i].y = b;
            e[i].val = c;
            G[a].push_back(b);
            G[b].push_back(a);
        }
        topw = 0;
        dfs_1(1,0,1);
        dfs_2(1,1);
        //debug();

        for(int i=1;i<N;i++)
        {
            if(dep[e[i].x] < dep[e[i].y]) swap(e[i].x,e[i].y);
            val[id[e[i].x]] = e[i].val;
        }

        Build(1,topw,1);
        char op[100];
        while(scanf("%s",op) && op[0] != 'D')
        {
            int a,b;
            scanf("%d%d",&a,&b);
            if(op[0] == 'Q')
                printf("%d
",Find(a,b));
            else if(op[0] == 'C')
                update(1,id[e[a].x],b);
        }

        for(int i=1;i<=N;i++) G[i].clear();
    }
}