【数据结构】Splay

struct Splay {

    static const int MAXN = 2e5 + 10;
    int top, root, ch[MAXN][2], pa[MAXN];
    int val[MAXN], cnt[MAXN], siz[MAXN];

    void _PushUp(int x) {
        siz[x] = siz[ch[x][0]] + siz[ch[x][1]] + cnt[x];
    }

    bool _Get(int x) {
        return x == ch[pa[x]][1];
    }

    void _Clear(int x) {
        ch[x][0] = 0, ch[x][1] = 0, pa[x] = 0;
        val[x] = 0, siz[x] = 0, cnt[x] = 0;
    }

    void _Rotate(int x) {
        int y = pa[x], z = pa[y], d = _Get(x);
        ch[y][d] = ch[x][d ^ 1], pa[ch[x][d ^ 1]] = y;
        ch[x][d ^ 1] = y, pa[y] = x, pa[x] = z;
        if(z)
            ch[z][y == ch[z][1]] = x;
        _PushUp(x), _PushUp(y);
    }

    void _Splay(int x) {
        for(int p = pa[x]; p = pa[x]; _Rotate(x)) {
            if(pa[p])
                _Rotate((_Get(x) == _Get(p)) ? p : x);
        }
        root = x;
    }

    void Init() {
        top = 0, root = 0;
    }

    void Insert(int v, int c = 1) {
        if(!root) {
            root = ++top;
            val[top] = v, cnt[top] = c;
            _PushUp(top);
            return;
        }
        int cur = root, p = 0;
        while(true) {
            if(val[cur] == v) {
                cnt[cur] += c;
                _PushUp(cur), _PushUp(p), _Splay(cur);
                break;
            }
            p = cur, cur = ch[cur][val[cur] < v];
            if(!cur) {
                ++top;
                val[top] = v, cnt[top] = c;
                pa[top] = p, ch[p][val[p] < v] = top;
                _PushUp(top), _PushUp(p), _Splay(top);
                break;
            }
        }
    }

    /* "Rank of value v" means the first node with value >= v */

    /* Get the rank of value v */
    int GetRank(int v) {
        int cur = root, res = 1;
        while(cur) {
            if(val[cur] > v)
                cur = ch[cur][0];
            else if(val[cur] == v) {
                res += siz[ch[cur][0]];
                _Splay(cur);
                break;
            } else {
                res += siz[ch[cur][0]] + cnt[cur];
                cur = ch[cur][1];
            }
        }
        return res;
    }

    /* Get the value with rank r */
    int GetValue(int r) {
        int cur = root, res = INF;
        while(cur) {
            if(siz[ch[cur][0]] >= r)
                cur = ch[cur][0];
            else if(siz[ch[cur][0]] + cnt[cur] >= r) {
                res = val[cur];
                _Splay(cur);
                break;
            } else {
                r -= siz[ch[cur][0]] + cnt[cur];
                cur = ch[cur][1];
            }
        }
        return res;
    }

    int _Prev() {
        int cur = ch[root][0];
        while(ch[cur][1])
            cur = ch[cur][1];
        _Splay(cur);
        return cur;
    }

    int GetPrev(int v) {
        Insert(v);
        int res = val[_Prev()];
        Remove(v);
        return res;
    }

    int _Next() {
        int cur = ch[root][1];
        while(ch[cur][0])
            cur = ch[cur][0];
        _Splay(cur);
        return cur;
    }

    int GetNext(int v) {
        Insert(v);
        int res = val[_Next()];
        Remove(v);
        return res;
    }

    void Remove(int v, int c = 1) {
        GetRank(v);
        if(val[root] != v)
            return;
        if(cnt[root] > c) {
            cnt[root] -= c;
            _PushUp(root);
            return;
        }
        if(ch[root][0] && ch[root][1]) {
            int cur = root, x = _Prev();
            pa[ch[cur][1]] = x, ch[x][1] = ch[cur][1];
            _Clear(cur), _PushUp(root);
            return;
        } else {
            int cur = root;
            root = ch[root][0] + ch[root][1], pa[root] = 0;
            _Clear(cur), _PushUp(root);
            return;
        }

    }

} splay;

【数据结构】Splay

原文：https://www.cnblogs.com/purinliang/p/14321732.html