AVL树

typedef struct node *pos;
typedef struct node *AvlT;

struct node
{
    int val;
    AvlT l;
    AvlT r;
    int h;
};

static int Height(pos p)
{
    if (!p) return -1;
    return p -> h;
}

static pos R_rotate(pos k2)
{
    pos k1;

    k1 = k2 -> l;
    k2 -> l = k1 -> r;
    k1 -> r = k2;

    k2 -> h = max(Height(k2 -> l), Height(k2 -> r)) + 1;
    k1 -> h = max(Height(k1 -> l), k2 -> h) + 1;

    return k1;
}

static pos L_rotate(pos k2)
{
    pos k1;

    k1 = k2 -> r;
    k2 -> r = k1 -> l;
    k1 -> l = k2;

    k2 -> h = max(Height(k2 -> l), Height(k2 -> r)) + 1;
    k1 -> h = max(Height(k1 -> l), k2 -> h) + 1;

    return k1;
}

static pos RL_rotate(pos k)
{
    k -> r = R_rotate(k -> r);  // 右旋变成 右-右型
    return L_rotate(k);
}

static pos LR_rotate(pos k)
{
    k -> l = L_rotate(k -> l);  // 左旋变成 左-左型
    return R_rotate(k);
}

AvlT inst(int x, AvlT t)
{
    if (!t)
    {
        t = (struct node*) malloc(sizeof (struct node));
        t -> val = x;
        t -> h = 0;     // 记得set树叶节点高度为0
        t -> l = t -> r = NULL;
        return t;
    }

    if (x < t -> val)
    {
        t -> l = inst(x, t -> l);
        if (Height(t -> l) - Height(t -> r) == 2)
            if (x < t -> l -> val)  // ll   右旋
                t = R_rotate(t);
            else                    // lr   左右旋
                t = LR_rotate(t);
    }

    else if (x > t -> val)
    {
        t -> r = inst(x, t -> r);
        if (Height(t -> r) - Height(t -> l) == 2)
            if (x > t -> r -> val)  // rr   左旋
                t = L_rotate(t);
            else                    // rl   右左旋
                t = RL_rotate(t);
    }

    t -> h = max(Height(t -> l), Height(t -> r)) + 1;
    return t;
}