[树链剖分] HDU 5893 List wants to travel

List wants to travel

题意：

给一棵树，每条边有个颜色，两种操作：

• Change a b c，把a到b的简单路径的边颜色变成c
• Query a b，查询a到b的简单路径有多少段颜色，连续相邻的同色边算一段。

思路：

先建立树剖然后用线段树维护，记录一个区间内的颜色段数，最左颜色和最右颜色，然后就可以区间合并了，需要注意合并的顺序，没想清楚很容易就wa了，我想的是总是按查询的时间顺序把区间挨个接起来，最后合并两边链的时候反转一个区间，接在另一个后面。

#include 
#include 
#include 
#include 
#include 
using namespace std;
const int NO = -0xdead;
const int N = 80005;
vector<int>G[N];
int sav[N][3];
int dep[N], fa[N], son[N], sz[N];
void dfs1(int rt) {
    sz[rt] = 1;
    for(int k = 0; k < G[rt].size(); ++k) {
        int v = G[rt][k];
        if(v == fa[rt]) continue;
        dep[v] = dep[rt]+1;
        fa[v] = rt;
        dfs1(v);
        sz[rt] += sz[v];
        if(son[rt] == 0 || sz[son[rt]] < sz[v]) son[rt] = v;
    }
}
int w[N], atw[N], top[N], wcnt;
void dfs2(int rt, int tp) {
    w[rt] = ++wcnt, atw[wcnt] = rt;
    top[rt] = tp;
    if(son[rt]) dfs2(son[rt], tp);
    for(int k = 0; k < G[rt].size(); ++k) {
        int v = G[rt][k];
        if(v == fa[rt] || v == son[rt]) continue;
        dfs2(v, v);
    }
}
struct node{
    int sum, l, r;
    node(){ sum = 0, l = NO, r = NO; }
    node operator + (const node& z) {
        node res;
        if(r == NO && z.l == NO) return res;
        if(r == NO && z.l != NO) return z;
        else if(r != NO && z.l == NO) return *this;
        res.sum = sum+z.sum;
        if(r == z.l) res.sum--;
        res.l = l, res.r = z.r;
        return res;
    }
}tree[N<<2];
int lazy[N<<2];
inline void push_down(int rt) {
    if(lazy[rt] != NO) {
        tree[rt<<1].sum = tree[rt<<1|1].sum = 1;
        tree[rt<<1].l = tree[rt<<1].r = lazy[rt];
        tree[rt<<1|1].l = tree[rt<<1|1].r = lazy[rt];
        lazy[rt<<1] = lazy[rt<<1|1] = lazy[rt];
        lazy[rt] = NO;
    }
}

void update(int rt, int l, int r, int ql, int qr, int v) {
    if(ql <= l && qr >= r) {
        tree[rt].sum = 1;
        tree[rt].l = tree[rt].r = v;
        lazy[rt] = v;
        return;
    }
    push_down(rt);
    int mid = (l+r) >> 1;
    if(ql <= mid) update(rt<<1, l, mid, ql, qr, v);
    if(qr > mid) update(rt<<1|1, mid+1, r, ql, qr, v);
    tree[rt] = tree[rt<<1] + tree[rt<<1|1];
}
node query(int rt, int l, int r, int ql, int qr) {
    if(ql <= l && qr >= r) {
        return tree[rt];
    }
    push_down(rt);
    node res; int mid = (l+r) >> 1;
    if(ql <= mid){
        res = res+query(rt<<1, l, mid, ql, qr);
    }
    if(qr > mid){
        res = res+query(rt<<1|1, mid+1, r, ql, qr);
    }
    tree[rt] = tree[rt<<1] + tree[rt<<1|1];
    return res;
}
int query(int va, int vb) {
    int f1 = top[va], f2 = top[vb];
    node a, b;
    while(f1 != f2) {
        if(dep[f1] > dep[f2]) {
            a = query(1, 1, wcnt, w[f1], w[va])+a;
            va = fa[f1], f1 = top[va];
        }
        else{
            b = query(1, 1, wcnt, w[f2], w[vb])+b;
            vb = fa[f2], f2 = top[vb];
        }
    }
    if(va == vb){
        swap(b.l, b.r);
        a = b+a;
        return a.sum;
    }
    if(dep[va] < dep[vb]) {
        b = query(1, 1, wcnt, w[son[va]], w[vb])+b;
        swap(b.l, b.r);
        a = b+a;
        return a.sum;
    }
    else {
        a = query(1, 1, wcnt, w[son[vb]], w[va])+a;
        swap(b.l, b.r);
        a = b+a;
        return a.sum;
    }
}
void update(int va, int vb, int v) {
    int f1 = top[va], f2 = top[vb];
    while(f1 != f2) {
        if(dep[f1] < dep[f2]){
            swap(f1, f2);
            swap(va, vb);
        }
        update(1, 1, wcnt, w[f1], w[va], v);
        va = fa[f1], f1 = top[va];
    }
    if(va == vb) return;
    if(dep[va] < dep[vb]) swap(va, vb);
    update(1, 1, wcnt, w[son[vb]], w[va], v);
}
char s[15];
int main() {
    int n, m;
    while(scanf("%d%d", &n, &m) != EOF) {
        for(int i = 1; i <= n; ++i) G[i].clear();
        for(int a, b, c, i = 1; i < n; ++i) {
            scanf("%d%d%d", &a, &b, &c);
            G[a].push_back(b);
            G[b].push_back(a);
            sav[i][0] = a, sav[i][1] = b, sav[i][2] = c;
        }
        memset(son, 0, sizeof(son));
        fa[1] = 0, dep[1] = 0;
        dfs1(1); wcnt = 0;
        dfs2(1, 1);
        for(int i = 1; i <= wcnt; ++i) {
            tree[i].sum = 0;
            tree[i].l = tree[i].r = NO;
            lazy[i] = NO;
        }
        for(int i = 1; i < n; ++i) {
            if(dep[sav[i][0]] > dep[sav[i][1]]) swap(sav[i][0], sav[i][1]);
            update(1, 1, wcnt, w[sav[i][1]], w[sav[i][1]], sav[i][2]);
        }
        while(m--) {
            scanf("%s", s);
            if(s[0] == 'Q') {
                int l, r;
                scanf("%d%d", &l, &r);
                if(l == r) { puts("0"); continue; }
                printf("%d\n", query(l, r));
            }
            else if(s[0] == 'C') {
                int l, r, v;
                scanf("%d%d%d", &l, &r, &v);
                update(l, r, v);
            }
        }
    }
    return 0;
}