hdu 3487 Play with Chain (Splay Tree easy)

acm.hdu.edu.cn/showproblem.php?pid=3487

　　再来一道Splay Tree的简单题，因为只用到两个基本操作，剪接和反转。虽说是简单题，可是我对细节稍有疏忽，所以我wa了几次。问题出在延迟标记的更新上，可能是半夜打代码的缘故，头脑有点不灵活，从而导致这种不容易debug出问题的错误，以后要多加注意这样的小问题！

AC代码：

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

using namespace std;
const int inf = 0x7f7f7f7f;

bool pnt;
struct Node {
    int key, cnt;
    bool rev;
    Node *c[2], *p;

    Node(int _key = 0, int _cnt = 0) {
        cnt = _cnt;
        key = _key;
        rev = false;
        c[0] = c[1] = p = NULL;
    }
} *Null, *Root;

void up(Node *rt) {
    rt->cnt = rt->c[0]->cnt + rt->c[1]->cnt + 1;
}

void down(Node *rt) {
    if (rt->rev) {
        Node *ls = rt->c[0], *rs = rt->c[1];

        if (ls != Null) {
            swap(ls->c[0], ls->c[1]);
            ls->rev = !ls->rev;
        }
        if (rs != Null) {
            swap(rs->c[0], rs->c[1]);
            rs->rev = !rs->rev;
        }
        rt->rev = false;
    }
}

void rotate(Node *x, bool right) {
    Node *y = x->p;

    down(y);
    down(x);
    y->c[!right] = x->c[right];
    if (x->c[right] != Null) {
        x->c[right]->p = y;
    }
    x->p = y->p;
    if (y->p != Null) {
        if (y->p->c[0] == y) y->p->c[0] = x;
        else y->p->c[1] = x;
    }
    x->c[right] = y;
    y->p = x;

    up(y);
    if (y == Root) Root = x;
}

void splay(Node *x, Node *f) {
    down(x);
    while (x->p != f) {
        if (x->p->p == f) {
            if (x->p->c[0] == x) rotate(x, 1);
            else rotate(x, 0);
        } else {
            Node *y = x->p, *z = y->p;

            if (z->c[0] == y) {
                if (y->c[0] == x) {
                    rotate(y, 1);
                    rotate(x, 1);
                } else {
                    rotate(x, 0);
                    rotate(x, 1);
                }
            } else {
                if (y->c[0] == x) {
                    rotate(x, 1);
                    rotate(x, 0);
                } else {
                    rotate(y, 0);
                    rotate(x, 0);
                }
            }
        }
    }

    up(x);
}

void inTra(Node *rt) {
    if (rt == Null) {
        return ;
    }
    down(rt);
    inTra(rt->c[0]);
    if (rt->key != inf){
        if (!pnt) pnt = true;
        else putchar(' ');
        printf("%d", rt->key);
    }
    inTra(rt->c[1]);
}

void initSplay() {
    Null = new Node();
    Root = new Node(inf, 1);

    Root->p = Root->c[0] = Null;
    Root->c[1] = new Node(inf, 1);
    Root->c[1]->p = Root;
    Root->c[1]->c[0] = Root->c[1]->c[1] = Null;
    up(Root);
}

void insSplay(int x) {
    Node *tmp = new Node(x, 1);

    tmp->c[1] = Root->c[1];
    Root->c[1]->p = tmp;
    Root->c[1] = tmp;
    tmp->p = Root;
    tmp->c[0] = Null;

    splay(tmp, Null);
}

Node *getNode(int pos) {
    Node *p = Root;

    pos++;
    while (true) {
        down(p);

        int cnt = p->c[0]->cnt;

//        printf("pos %d  cnt %d\n", pos, cnt);
        if (pos == cnt + 1) {
            return p;
        } else if (pos <= cnt) {
            p = p->c[0];
        } else {
            pos -= cnt + 1;
            p = p->c[1];
        }
    }
}

void cutSeg(int l, int r, int pos) {
    Node *pl = getNode(l - 1);
    splay(pl, Null);
    Node *pr = getNode(r + 1);
    splay(pr, pl);

//    inTra(Root);
//    puts("!!!");

    // cut segment
    Node *tmp = pr->c[0];

    down(tmp);
    pr->c[0] = Null;
    splay(pr, Null);
    // insert segment
//    printf("pos %d\n", pos);
//    inTra(Root);
//    puts("~~~");
    pl = getNode(pos);
    splay(pl, Null);
    pr = getNode(pos + 1);
    splay(pr, pl);
//    puts("cut??");

    pr->c[0] = tmp;
    tmp->p = pr;
    splay(tmp, Null);
}

void reverse(int l, int r) {
    Node *pl = getNode(l - 1);
    splay(pl, Null);
    Node *pr = getNode(r + 1);
    splay(pr, pl);

    pr = pr->c[0];
    down(pr);
    pr->rev = true;
    swap(pr->c[0], pr->c[1]);
    splay(pr, Null);
}

void build(int n) {
    initSplay();
    for (int i = 1; i <= n; i++) {
        insSplay(i);
    }
}

void process(int m) {
    char buf[5];
    int l, r, pos;

    while (m--) {
        scanf("%s", buf);
        if (buf[0] == 'C') {
            scanf("%d%d%d", &l, &r, &pos);
            if (l > r) swap(l, r);
            cutSeg(l, r, pos);
//            puts("cut~");
        } else {
            scanf("%d%d", &l, &r);
            if (l > r) swap(l, r);
            reverse(l, r);
//            puts("flip~");
        }
    }
}

void delSplay(Node *rt) {
    if (rt == Null) {
        return ;
    } else {
        delSplay(rt->c[0]);
        delSplay(rt->c[1]);
        delete rt;
    }
}

int main() {
    int n, m;

//    freopen("in", "r", stdin);
//    freopen("out", "w", stdout);
    while (~scanf("%d%d", &n, &m) && (n >= 0 || m >= 0)) {
        build(n);
//        inTra(Root);
//        puts("built!");
        process(m);
//        puts("processed!");
        pnt = false;
        inTra(Root);
        puts("");
        delSplay(Root);
        delete Null;
    }

    return 0;
}

——written by Lyon