Method insert

templates/red-black-tree.cpp:153–170

    }

    void insert(RBTreeNode* z)
    {
        auto y = nil;
        auto x = root;
        // 找到父节点
        while (x != nil) {
            y = x;
            if (z->k < x->k) {
                x = x->left;
            } else {
                x = x->right;
            }
        }

        z->p = y;
        y->addChild(this, z);
        insertFixup(z);
    }

    /*
    1 父子节点之间不能出现两个连续的红节点