POJ 3728 tarjan+DP

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从这个好题我终于去学了学Tarjan, 因为发现ST毫无意义，除了预处理，其他还是要借鉴Tarjan；
Tarjan其实很简单，其实就是对于询问也开一个邻接表，两个点的LCA就是：
如果在访问u的时候发现v已经访问过了，那么LCA就是find（u）
至于这个题up， down， max， min的作用就不说了，网上的主流代码
是个好题，初学Tarjan一定要去搞

#include <vector>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;#define N 400010#define next Next#define begin Begin#define pb push_back#define mem(a, b) memset(a, b, sizeof(a))#define rep(i, s, t) for(int i = s, end = t; i <= end; ++i)#define erep(i, u) for(int i = begin[u]; i != -1; i = next[i])bool vis[N];int to[N], next[N], begin[N], n, m, q;int e, res[N], w[N];int mx[N], mn[N], up[N], down[N], fa[N];vector<int> query[N], s[N];void add(int u, int v) {    to[++e] = v;    next[e] = begin[u];    begin[u] = e;}int find(int x) {    if(x == fa[x]) return x;    int y = fa[x];    fa[x] = find(fa[x]);    up[x] = max(mx[y] - mn[x], max(up[x], up[y]));    down[x] = max(mx[x] - mn[y], max(down[x], down[y]));    mx[x] = max(mx[x], mx[y]);    mn[x] = min(mn[x], mn[y]);    return fa[x];}void LCA(int u) {    int v;    vis[u] = 1;    for(int i = 0; i < (int) query[u].size(); i += 2)        if(vis[v = query[u][i]]) {            int f = find(v), id = query[u][i+1];            if(id > 0) s[f].pb(u), s[f].pb(v);            else s[f].pb(v), s[f].pb(u);            s[f].pb(id > 0? id : -id);        }    erep(i, u)         if(!vis[v = to[i]]){            LCA(v);            fa[v] = u;        }    for(int i = 0; i < (int)s[u].size(); i += 3) {        int x = s[u][i], y = s[u][i+1], id = s[u][i+2];        find(x); find(y);        res[id] = max(up[x], max(down[y], mx[y] - mn[x]));    }}void init() {    e = 0;    mem(up, 0); mem(down, 0);    mem(vis, 0);    mem(begin, -1);    rep(i, 0, n) fa[i] = i, s[i].clear(), query[i].clear();}int main() {#ifndef ONLINE_JUDGE    freopen("data.in", "r", stdin);    freopen("result.out", "w", stdout);#endif    scanf("%d", &n);    init();    rep(i, 1, n) {        scanf("%d", &w[i]);        mx[i] = w[i];        mn[i] = w[i];     }    rep(i, 1, n-1) {        int u, v;        scanf("%d%d", &u, &v);        add(u, v); add(v, u);    }    scanf("%d", &m);    rep(i, 1, m) {        int u, v;        scanf("%d%d", &u, &v);        query[u].pb(v);        query[u].pb(i);        query[v].pb(u);        query[v].pb(-i);    }    LCA(1);    rep(i, 1, m) printf("%d\n", res[i]);    /*puts("%----------------%");    rep(i, 1, n)         printf("%d %d %d %d\n", up[i], down[i], mx[i], mn[i]);        */    return 0;}

VECTOR巨慢。。。。

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