Visit Counter
AmazingCounters.com

1、感谢taorunz老师
2、题目大意:就是给个带权无向图,然后有两种操作,
1是修改某个点的权值
2是询问,询问一个值,就是u到v之间经过点权的最小值(不可以经过重复的点)
操作数,点数,边数都不超过100000
3、分析:首先看这道题,就感觉用双联通+树剖搞一搞可以过,可是怎么搞呢
首先双联通是必然的了,可是正常的缩点+树剖会爆零随便试试就知道了
然后我们需要不正常的缩点,我们在正常的缩点后加入割点,割点向它所属的一切双联通分量连边
这样,我们就不怕询问的u和v中有割点了,可是虽然询问是logn*logn了,但是修改会超时,于是我们想想应该怎么搞呢
taorunz告诉我说,图会满足一个性质,块的父亲是割点,割点的父亲是块,我们维护块的值是,
这个块所代表的双联通,除了它父亲的那个割点,那么我们这么修改,如果修改的非割点,就正常修改,
如果是割点,那么它的父亲这个块也要修改,这样修改就是o(logn)了,我们就可以过了,但是树剖的询问中
如果lca是块,我们还要询问这个块的父亲,这样,这道题就完美的AC了,(各种bug
4、代码:

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <stack>
using namespace std;
struct node{
    int from, to, next;
} G[2000010];
struct segment_tree{
    int q[50000010];
    int x, y;
    inline void init(){
        for(int i = 1; i <= 4500000; i ++) q[i] = 2147483647;
        return;
    }
    inline void add(int l, int r, int o){
        if(l == r && l == x){
            q[o] = y;
            return;
        }
        int mid = (l + r) / 2;
        if(x <= mid) add(l, mid, 2 * o);
        if(x > mid) add(mid + 1, r, 2 * o + 1);
        q[o] = q[2 * o];
        if(q[2 * o + 1] < q[o]) q[o] = q[2 * o + 1];
        return;
    }
    inline int query(int l, int r, int o){
        if(x <= l && r <= y){
            return q[o];
        }
        int mid = (l + r) / 2;
        int ret = 2147483647;
        if(x <= mid){
            int wl = query(l, mid, 2 * o);
            if(wl < ret) ret = wl;
        }
        if(y > mid){
            int wl = query(mid + 1, r, 2 * o + 1);
            if(wl < ret) ret = wl;
        }
        return ret;
    }
} qzh, mmd;
struct tree_chain_paritition{
    int Top[2000010];
    int Size[2000010];
    int Height[2000010];
    int Father[2000010];
    int Num[2000010];
    int value[2000010];
    node G[2000010];
    int head[2000010], ff, de, n;
    int vis[2000010];
    int is_cut[2000010];
    inline void for_tree(){
        for(int i = 1; i <= n; i ++) is_cut[i] = 1;
    }
    inline void init(){
        memset(is_cut, 0, sizeof(is_cut));
        memset(head, -1, sizeof(head));
        de = 0;
    }
    inline void insert(int u, int v){
        //printf("%d %d\n", u, v);
        ff ++;
        G[ff] = (node){u, v, head[u]};
        head[u] = ff;
        return;
    }
    inline void dfs1(int u, int fa, int k){
        Father[u] = fa;
        Height[u] = k;
        Size[u] = 1;
        vis[u] = 1;
        for(int i = head[u]; i != -1; i = G[i].next){
            node e = G[i];
            if(!vis[e.to]){
                dfs1(e.to, u, k + 1);
                Size[u] += Size[e.to];
            }
        }
        return;
    }
    inline void dfs2(int u, int fa){
        vis[u] = 1;
        int o = 0, pos;
        for(int i = head[u]; i != -1; i = G[i].next){
            node e = G[i];
            if(!vis[e.to]){
                if(Size[e.to] > o){
                    pos = i;
                    o = Size[e.to];
                }
            }
        }
        if(o != 0){
            node e = G[pos];
            qzh.x = ++ de;
            qzh.y = value[e.to];
            qzh.add(1, n, 1);
            Top[e.to] = Top[u];
            Num[e.to] = de;
            dfs2(e.to, u);
        }
        for(int i = head[u]; i != -1; i = G[i].next){
            node e = G[i];
            if(!vis[e.to] && i != pos){
                qzh.x = ++ de;
                qzh.y = value[e.to];
                qzh.add(1, n, 1);
                Top[e.to] = e.to;
                Num[e.to] = de;
                dfs2(e.to, u);
            }
        }
        return;
    }
    inline void solve(){
        qzh.x = ++ de;
        qzh.y = value[1];
        qzh.add(1, n, 1);
        Top[1] = 1;
        Num[1] = de;
        memset(vis, 0, sizeof(vis));
        dfs2(1, 0);
        return;
    }
    inline void change(int s, int t){
        qzh.x = Num[s];
        qzh.y = t;
        qzh.add(1, n, 1);
        return;
    }
    inline int qmin(int s, int t){
        int ret = 2147483647;
        while(Top[s] != Top[t]){
            if(Height[Top[s]] > Height[Top[t]]) swap(s, t);
            qzh.x = Num[Top[t]];
            qzh.y = Num[t];
            int wl = qzh.query(1, n, 1);
            if(wl < ret) ret = wl;
            t = Father[Top[t]];
        }
        if(Height[s] > Height[t]) swap(s, t);
        qzh.x = Num[s];
        qzh.y = Num[t];
        int wl = qzh.query(1, n, 1);
        if(wl < ret) ret = wl;
        if(!is_cut[s] && s != 1){
            qzh.x = Num[Father[s]];
            qzh.y = Num[Father[s]];
            wl = qzh.query(1, n, 1);
            if(wl < ret) ret = wl;
        }
        return ret;
    }
    inline void debug(){
        printf("\nNum:");
        for(int i = 1; i <= n; i ++) printf("%d ", Num[i]);
        printf("\nSize:");
        for(int i = 1; i <= n; i ++) printf("%d ", Size[i]);
        printf("\nHeight:");
        for(int i = 1; i <= n; i ++) printf("%d ", Height[i]);
        printf("\nTop:");
        for(int i = 1; i <= n; i ++) printf("%d ", Top[i]);
        printf("\n");
    }
} wt;
int first[2000010], Next[2000010], poss[2000010], Left[2000010], Right[2000010];
int labccno[2000010];
int ff;
int w[2000010];
int head[2000010], next[2000010];
int pre[2000010], iscut[2000010], bccno[2000010], use_times[2000010];
int head1[2000010], next1[2000010], kt[2000010];
int vis[2000010];
int dfs_clock, bcc_cnt;
int dark;
int he[2000010], ne[2000010];
int poss_fa[2000010];
stack<node> S;
inline int dfs(int u, int fa);
inline void insert(int u, int v);
int main(){
    int n, m, q;
    while(scanf("%d%d%d", &n, &m, &q) != EOF){
        memset(head, -1, sizeof(head));
        memset(first, -1, sizeof(first));
        memset(head1, -1, sizeof(head1));
        memset(iscut, 0, sizeof(iscut));
        memset(he, -1, sizeof(he));
        for(int i = 1; i <= n; i ++){
            scanf("%d", &w[i]);
        }
        for(int i = 1; i <= m; i ++){
            int u, v;
            scanf("%d%d", &u, &v);
            insert(u, v);
            insert(v, u);
        }
        dfs_clock = bcc_cnt = 0;
        for(int i = 1; i <= n; i ++){
            if(!pre[i]) int wl = dfs(i, -1);
        }
        for(int i = 1; i <= n; i ++) labccno[i] = bccno[i];
        /*for(int i = 1; i <= n; i ++){
            printf("%d ", bccno[i]);
        }
        printf("\n");*/
        for(int i = 1; i <= n; i ++){
            if(iscut[i]){
                bcc_cnt ++;
                bccno[i] = bcc_cnt;
            }
        }
        qzh.init();
        wt.init();
        wt.n = bcc_cnt;
        for(int i = 1; i <= bcc_cnt; i ++) wt.value[i] = 2147483647;
        for(int i = 1; i <= n; i ++){
            wt.value[bccno[i]] = min(wt.value[bccno[i]], w[i]);
        }
        memset(vis, 0, sizeof(vis));
        /*for(int i = 1; i <= n; i ++){
            printf("%d ", bccno[i]);
        }
        printf("\n");*/
        for(int i = 1; i <= n; i ++){
            if(iscut[i]){
                for(int j = head1[i]; j != -1; j = next1[j]){
                    wt.insert(bccno[i], kt[j]);
                    wt.insert(kt[j], bccno[i]);
                    //wt.value[kt[j]] = min(wt.value[kt[j]], w[i]);
                }
            }
            else{
                for(int j = head[i]; j != -1; j = G[j].next){
                    int ii = bccno[i], jj = bccno[G[j].to];
                    if(ii != jj){
                        wt.insert(ii, jj);
                        wt.insert(jj, ii);
                    }
                }   
            }
        }
        memset(wt.vis, 0, sizeof(wt.vis));
        wt.dfs1(1, 0, 1);
        int N = n;
        for(int i = 1; i <= n; i ++) if(iscut[i]){
            N ++;
            ne[i] = he[wt.Father[bccno[i]]];
            he[wt.Father[bccno[i]]] = i;
            wt.is_cut[bccno[i]] = 1;
            wt.value[wt.Father[bccno[i]]] = min(wt.value[wt.Father[bccno[i]]], w[i]);
        }
        wt.solve();
        mmd.init();
        int yy = 0;
        for(int i = 1; i <= n; i ++){
            Next[i] = first[bccno[i]];
            first[bccno[i]] = i;
        }
        for(int i = 1; i <= bcc_cnt; i ++){
            Left[i] = yy + 1;
            for(int j = first[i]; j != -1; j = Next[j]){
                ++ yy;
                mmd.x = yy;
                mmd.y = w[j];
                mmd.add(1, N, 1);
                poss[j] = yy;
            }
            for(int j = he[i]; j != -1; j = ne[j]){
                ++ yy;
                mmd.x = yy;
                mmd.y = w[j];
                mmd.add(1, N, 1);
                poss_fa[j] = yy;
            }
            Right[i] = yy;
        }
        /*for(int i = 1; i <= n; i ++){
            printf("%d ", bccno[i]);
        }
        printf("\n");*/
        //if(m < n) wt.for_tree();
    //    wt.debug();
        for(int i = 1; i <= q; i ++){
            char str[5];
            int u, v;
            scanf("%s%d%d", str, &u, &v);
            if(str[0] == 'C'){
                w[u] = v;
                mmd.x = poss[u];
                mmd.y = v;
                mmd.add(1, N, 1);
                mmd.x = Left[bccno[u]];
                mmd.y = Right[bccno[u]];
                int st = mmd.query(1, N, 1);
                wt.change(bccno[u], st);
                if(iscut[u]){
                    mmd.x = poss_fa[u];
                    mmd.y = v;
                    mmd.add(1, N, 1);
                    mmd.x = Left[wt.Father[bccno[u]]];
                    mmd.y = Right[wt.Father[bccno[u]]];
                    int st = mmd.query(1, N, 1);
                    wt.change(wt.Father[bccno[u]], st);
                }
            }
            else{
                if(u == v) printf("%d\n", w[u]);
                else printf("%d\n", wt.qmin(bccno[u], bccno[v]));
            }
        }   
    }
    return 0;
}
inline void insert(int u, int v){
    ff ++;
    G[ff] = (node){u, v, head[u]};
    head[u] = ff;
    return;
}
inline int dfs(int u, int fa){
    int lowu = pre[u] = ++ dfs_clock;
    int child = 0;
    for(int i = head[u]; i != -1; i = G[i].next){
        node e = G[i];
        if(!pre[e.to]){
            S.push(e);
            child ++;
            int lowv = dfs(e.to, u);
            lowu = min(lowu, lowv);
            if(lowv >= pre[u]){
                iscut[u] = true;
                bcc_cnt ++;
                for(; ; ){
                    node h = S.top(); S.pop();
                    if(bccno[h.from] != bcc_cnt) {
                        next1[++ dark] = head1[h.from];
                        head1[h.from] = dark;
                        kt[dark] = bcc_cnt;
                        bccno[h.from] = bcc_cnt;
                        use_times[h.from] ++;
                    }
                    if(bccno[h.to] != bcc_cnt){
                        next1[++ dark] = head1[h.to];
                        head1[h.to] = dark;
                        kt[dark] = bcc_cnt;
                        bccno[h.to] = bcc_cnt;
                        use_times[h.to] ++;
                    }
                    if(h.from == u && h.to == e.to){
                        break;
                    }
                }
            }
        }
        else if(pre[e.to] < pre[u] && e.to != fa){
            S.push(e);
            lowu = min(lowu, pre[e.to]);
        }
    }
    if(fa < 0 && child == 1) iscut[u] = 0;
    return lowu;
}