【SPOJ】375 Query on a tree

#include<cstdio>
#include<cstring>
#include<queue>
#include<iostream>
#include<algorithm>
#define MAXN 10010
#define MAXM 20010
#define oo 0x7FFFFFFF
using namespace std;
int first[MAXN], next[MAXM], v[MAXM], cost[MAXM], e;
bool vis[MAXN];
struct LCT {
    int next[MAXN][2], pre[MAXN], val[MAXN], belong[MAXN], bef[MAXN], key[MAXN];
    void Init() {
        memset(next, 0, sizeof(next));
        memset(pre, 0, sizeof(pre));
        val[0] = key[0] = -oo;
    }
    inline void PushUp(int x) {
        val[x] = max(key[x], max(val[next[x][0]], val[next[x][1]]));
    }
    inline void Rotate(int x, int kind) {
        int y, z;
        y = pre[x];
        z = pre[y];
        next[y][!kind] = next[x][kind];
        pre[next[x][kind]] = y;
        next[z][next[z][1] == y] = x;
        pre[x] = z;
        next[x][kind] = y;
        pre[y] = x;
        PushUp(y);
    }
    void Splay(int x) {
        int rt;
        for (rt = x; pre[rt]; rt = pre[rt])
            ;
        if (rt != x) {
            bef[x] = bef[rt];
            bef[rt] = 0;
            while (pre[x]) {
                if (next[pre[x]][0] == x)
                    Rotate(x, 1);
                else
                    Rotate(x, 0);
            }
            PushUp(x);
        }
    }
    void Access(int x) {
        int father;
        for (father = 0; x; x = bef[x]) {
            Splay(x);
            bef[next[x][1]] = x;
            bef[father] = 0;
            pre[next[x][1]] = 0;
            next[x][1] = father;
            pre[father] = x;
            father = x;
            PushUp(x);
        }
    }
    int Query(int x, int y) {
        Access(y);
        for (y = 0; x; x = bef[x]) {
            Splay(x);
            if (!bef[x])
                return max(val[y], val[next[x][1]]);
            bef[next[x][1]] = x;
            bef[y] = 0;
            pre[next[x][1]] = 0;
            next[x][1] = y;
            pre[y] = x;
            y = x;
            PushUp(x);
        }
        return 0;
    }
    void Change(int x, int y) {
        int t;
        t = belong[x - 1];
        key[t] = y;
        Splay(t);
    }
} lct;
int INT() {
    int res;
    char ch;
    bool neg;
    while (ch = getchar(), !isdigit(ch) && ch != '-')
        ;
    if (ch == '-') {
        neg = true;
        res = 0;
    } else {
        neg = false;
        res = ch - '0';
    }
    while (ch = getchar(), isdigit(ch))
        res = res * 10 + ch - '0';
    return neg ? -res : res;
}
char CHAR() {
    char res, ch;
    while (res = getchar(), !isalpha(res))
        ;
    while (ch = getchar(), isalpha(ch))
        ;
    return res;
}
inline void AddEdge(int x, int y, int val) {
    v[e] = y;
    cost[e] = val;
    next[e] = first[x];
    first[x] = e++;
}
void BFS(int x) {
    int i, y;
    queue<int> q;
    memset(vis, false, sizeof(vis));
    vis[x] = true;
    q.push(x);
    while (!q.empty()) {
        x = q.front();
        q.pop();
        for (i = first[x]; i != -1; i = next[i]) {
            y = v[i];
            if (!vis[y]) {
                lct.bef[y] = x;
                lct.key[y] = lct.val[y] = cost[i];
                lct.belong[i >> 1] = y;
                vis[y] = true;
                q.push(y);
            }
        }
    }
}
int main() {
    int c;
    char ch;
    int n, i;
    int u, v, w;
    c = INT();
    while (c--) {
        lct.Init();
        n = INT();
        memset(first, -1, sizeof(first));
        for (e = 0, i = 1; i < n; i++) {
            u = INT(), v = INT(), w = INT();
            AddEdge(u, v, w);
            AddEdge(v, u, w);
        }
        BFS(1);
        while (ch = CHAR(), ch != 'D') {
            u = INT(), v = INT();
            if (ch == 'Q')
                printf("%d\n", lct.Query(u, v));
            else
                lct.Change(u, v);
        }
    }
    return 0;
}