题目链接：uva 1479 - Graph and Queries

题目大意：有一张m条边的无向图，每个节点都有一个权值，现在有若干个操作，

• D x：删除ID为x的节点
• Q x k：计算与节点x联通的节点当中，第k大的权值
• C x v：把节点x的权值改为v

解题思路：把所有操作反过来处理，先执行所有的D操作，获得最终的图，然后逆操作的时候对于D来说即为合并操作，Q和C则是查询和修改操作。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <algorithm>

using namespace std;

typedef long long ll;
const int maxn = 20005;
const int maxm = 60005;
const int maxc = 500005;

// Union-Set
int f[maxn];
inline int getfar(int x) {
    return x == f[x] ? x : f[x] = getfar(f[x]);
}

// Treap;
struct Node {
    int val, rank, sum;
    Node* cid[2];

    Node (int val);
    void maintain();
    int cmp(int x);
};
Node* root[maxn];

void insert(Node* &o, int x);
void rotate(Node* &o, int d);
void remove(Node* &o, int x);

// Rank Tree;
void add_edge (int i);
void remove_tree(Node* &o);
void merge_tree(Node* &src, Node* & dest);
int rankth(Node* o, int k);

// Command;
struct Command {
    char type;
    int x, p;
}command[maxc];

bool flag[maxm];
ll tot, cnt;
int N, M, C, W[maxn], U[maxm], V[maxm];

void build () {
    for (int i = 1; i <= N; i++) {
        if (root[i] != NULL)
            remove_tree(root[i]);
        root[i] = new Node(W[i]);
    }

    for (int i = 1; i <= M; i++) {
        if (!flag[i])
            add_edge(i);
    }
}

void init () {
    C = 0;
    memset(flag, 0, sizeof(flag));
    for (int i = 1; i <= N; i++) {
        f[i] = i;
        scanf("%d", &W[i]);
    }

    for (int i = 1; i <= M; i++)
        scanf("%d%d", &U[i], &V[i]);

    int x, p;
    char str[5];
    while (scanf("%s", str) == 1 && str[0] != ‘E‘) {
        scanf("%d", &x);

        if (str[0] == ‘D‘) flag[x] = 1;
        else if (str[0] == ‘Q‘) scanf("%d", &p);
        else if (str[0] == ‘C‘) {
            scanf("%d", &p);
            swap(p, W[x]);
        }
        command[C++] = (Command){ str[0], x, p};
    }

    build();
}

void query (int x, int k) {
    cnt++;
    tot += rankth(root[getfar(x)], k);
}

void change (int x, int v) {
    int u = getfar(x);
    remove(root[u], W[x]);
    insert(root[u], v);
    W[x] = v;
}

int main () {
    int cas = 0;
    while (scanf("%d%d", &N, &M) == 2 && N) {
        init();
        tot = cnt = 0;

        for (int i = C - 1; i >= 0; i--) {
            char type = command[i].type;
            if (type == ‘D‘)
                add_edge(command[i].x);
            else if (type == ‘Q‘)
                query(command[i].x, command[i].p);
            else
                change(command[i].x, command[i].p);
        }
        printf("Case %d: %.6lf\n", ++cas, tot / (double) cnt);
    }
    return 0;
}

// Rank Tree;
int rankth(Node* o, int k) {
    if (o == NULL || k <= 0 || k > o->sum)
        return 0;
    int s = (o->cid[1] == NULL ? 0 : o->cid[1]->sum);

    if (k == s + 1) return o->val;
    else if (k <= s) return rankth(o->cid[1], k);
    else return rankth(o->cid[0], k - s - 1);
}

void remove_tree (Node* &o) {
    for (int i = 0; i < 2; i++) {
        if (o->cid[i] != NULL)
            remove_tree(o->cid[i]);
    }
    delete o;
    o = NULL;
}

void add_edge (int x) {
    int u = getfar(U[x]), v = getfar(V[x]);

    if (u != v) {
        if (root[u]->sum < root[v]->sum)
            swap(u, v);
        f[v] = u;
        merge_tree(root[v], root[u]);
    }
}

void merge_tree (Node* &src, Node* &dest) {
    for (int i = 0; i < 2; i++) {
        if (src->cid[i] != NULL)
            merge_tree(src->cid[i], dest);
    }
    insert(dest, src->val);
    delete src;
    src = http://www.mamicode.com/NULL;"hljs-comment" style="color:rgb(117,113,94)">// Treap
Node::Node (int val) {
    sum = 1;
    rank = rand();
    this->val = val;
    cid[0] = cid[1] = NULL;
}

void Node::maintain() {
    sum = 1;
    if (cid[0] != NULL) sum += cid[0]->sum;
    if (cid[1] != NULL) sum += cid[1]->sum;
}

int Node::cmp(int x) {
    if (val == x)
        return -1;
    return val < x ? 1 : 0;
}

void remove(Node* &o, int x) {
    int d = o->cmp(x);
    if (d == -1) {
        Node* u = o;
        if (o->cid[0] != NULL && o->cid[1] != NULL) {
            int d2 = (o->cid[0]->rank > o->cid[1]->rank ? 1 : 0);
            rotate(o, d2);
            remove(o->cid[d2], x);
        } else {
            o = (o->cid[0] == NULL ? o->cid[1] : o->cid[0]);
            delete u;
        }
    } else
        remove(o->cid[d], x);

    if (o != NULL)
        o->maintain();
}

void rotate (Node* &o, int d) {
    Node* k = o->cid[d^1];
    o->cid[d^1] = k->cid[d];
    k->cid[d] = o;
    o->maintain();
    k->maintain();
    o = k;
}

void insert(Node* &o, int x) {
    if (o == NULL)
        o = new Node(x);
    else {
        int d = (x < o->val ? 0 : 1);
        insert(o->cid[d], x);
        if (o->cid[d]->rank > o->rank)
            rotate(o, d^1);
    }
    o->maintain();
}

uva 1479 - Graph and Queries(伸展树)