Ultraviolet A 11354-bond (tree link Division)

Link to the question: Ultraviolet A 11354-Bond

Given a graph, each time you ask the minimum value of the dangerous value of the crossing edge on two node paths.

Solution: first, create the minimum number of generations, and then split the tree chains based on the tree.

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int maxn = 50005;const int INF = 0x3f3f3f3f;struct Edge {    int u, v, w;    Edge (int u = 0, int v = 0, int w = 0) { set(u, v, w); }    void set(int u, int v, int w) {        this->u = u;        this->v = v;        this->w = w;    }    friend bool operator < (const Edge& a, const Edge& b) {        return a.w < b.w;    }}ed[maxn * 2];int N, M, Q, ne, f[maxn], first[maxn], jump[maxn * 2], val[maxn];int id, idx[maxn], top[maxn], far[maxn], son[maxn], dep[maxn], cnt[maxn];vector<Edge> vec;inline int getfar(int x) {    return x == f[x] ? x : f[x] = getfar(f[x]);}inline void add_Edge (int u, int v, int w) {    ed[ne].set(u, v, w);    jump[ne] = first[u];    first[u] = ne++;}void dfs (int u, int pre, int d) {    far[u] = pre;    dep[u] = d;    son[u] = 0;    cnt[u] = 1;    for (int i = first[u]; i + 1; i = jump[i]) {        int v = ed[i].v;        if (v == pre)            continue;        dfs(v, u, d + 1);        cnt[u] += cnt[v];        if (cnt[son[u]] < cnt[v])            son[u] = v;    }}void dfs (int u, int rot) {    top[u] = rot;    idx[u] = ++id;    if (son[u])        dfs(son[u], rot);    for (int i = first[u]; i + 1; i = jump[i]) {        int v = ed[i].v;        if (v == far[u] || v == son[u])            continue;        dfs(v, v);    }}#define lson(x) ((x)<<1)#define rson(x) (((x)<<1)|1)int lc[maxn << 2], rc[maxn << 2], s[maxn << 2];inline void pushup(int u) {    s[u] = max(s[lson(u)], s[rson(u)]);}void build (int u, int l, int r) {    lc[u] = l;    rc[u] = r;    if (l == r) {        s[u] = val[l];        return;    }    int mid = (l + r) / 2;    build(lson(u), l, mid);    build(rson(u), mid + 1, r);    pushup(u);}int query(int u, int l, int r) {    if (l <= lc[u] && rc[u] <= r)        return s[u];    int mid = (lc[u] + rc[u]) / 2, ret = 0;    if (l <= mid)        ret = max(ret, query(lson(u), l, r));    if (r > mid)        ret = max(ret, query(rson(u), l, r));    return ret;}void init () {    int u, v, w;    ne = id = 0;    vec.clear();    memset(first, -1, sizeof(first));    for (int i = 1; i <= N; i++)        f[i] = i;    for (int i = 0; i < M; i++) {        scanf("%d%d%d", &u, &v, &w);        vec.push_back(Edge(u, v, w));    }    sort(vec.begin(), vec.end());    for (int i = 0; i < vec.size(); i++) {        int p = getfar(vec[i].u);        int q = getfar(vec[i].v);        if (p == q)            continue;        add_Edge(vec[i].u, vec[i].v, vec[i].w);        add_Edge(vec[i].v, vec[i].u, vec[i].w);        f[p] = q;    }    dfs(1, 0, 0);    dfs(1, 1);    for (int i = 0; i < N - 1; i++) {        int t = i * 2;        u = (dep[ed[t].u] < dep[ed[t].v] ? ed[t].v : ed[t].u);        val[idx[u]] = ed[t].w;    }    build(1, 1, N);}int solve (int u, int v) {    int p = top[u], q = top[v], ret = 0;    while (p != q) {        if (dep[p] < dep[q]) {            swap(p, q);            swap(u, v);        }        ret = max(ret, query(1, idx[p], idx[u]));        u = far[p];        p = top[u];    }    if (u == v)        return ret;    if (dep[u] > dep[v])        swap(u, v);    ret = max(ret, query(1, idx[son[u]], idx[v]));    return ret;}int main () {    int cas = 0;    while (scanf("%d%d", &N, &M) == 2) {        if (cas++)            printf("\n");        init();        int u, v;        scanf("%d", &Q);        while (Q--) {            scanf("%d%d", &u, &v);            printf("%d\n", solve(u, v));        }    }    return 0;}

Ultraviolet A 11354-bond (tree link Division)