Exemplo n.º 1
0
    private void fixAfterDeletion(int parentIndex) {
      if (isRoot() || parent.isRoot()) return; // No fixing needed

      if (parent.nrElements < MIN) { // If parent lost it's n/2 element repair it
        BTreeNode temp = parent;
        temp.prepareForDeletion(parentIndex);
        if (temp.parent == null) return; // Root changed
        if (!temp.parent.isRoot() && temp.parent.nrElements < MIN) { // If need be recurse
          BTreeNode x = temp.parent.parent;
          int i = 0;
          // Find parent's parentIndex
          for (; i < entries.length; i++) if (x.entries[i].child == temp.parent) break;
          temp.parent.fixAfterDeletion(i);
        }
      }
    }
Exemplo n.º 2
0
    /*
     * This method is called only when stealLeft, stealRight, and mergeLeft could not be called,
     * the BTreeNode has the minimum number of elements, has a rightSibling, and the
     * rightSibling has more than the minimum number of elements.  If after completion
     * parent has fewer than the minimum number of elements than the parents entries[0]
     * slot is left empty in anticipation of a recursive call to stealLeft, stealRight,
     * mergeLeft, or mergeRight to fix the parent. All of the before-mentioned methods
     * expect the parent to be in such a condition.
     */
    private void mergeRight(int parentIndex) {
      BTreeNode p = parent;
      BTreeNode rs = p.entries[parentIndex + 1].child;

      if (isLeaf()) { // Don't worry about children
        entries[nrElements] = new Entry();
        entries[nrElements].element = p.entries[parentIndex].element;
        nrElements++;
        for (int i = 0, nr = nrElements; i < rs.nrElements; i++, nr++) {
          entries[nr] = rs.entries[i];
          nrElements++;
        }
        p.entries[parentIndex].element = p.entries[parentIndex + 1].element;
        if (p.nrElements == MIN && p != BTreeSet.this.root) {
          for (int x = parentIndex + 1, y = parentIndex; y >= 0; x--, y--)
            p.entries[x] = p.entries[y];
          p.entries[0] = new Entry();
          p.entries[0].child =
              rs; // So it doesn't think it's a leaf, this child will be deleted in the next
          // recursive call
        } else {
          for (int x = parentIndex + 1, y = parentIndex + 2; y <= p.nrElements; x++, y++)
            p.entries[x] = p.entries[y];
          p.entries[p.nrElements] = null;
        }

        p.nrElements--;
        if (p.isRoot() && p.nrElements == 0) { // It's the root and it's empty
          BTreeSet.this.root = this;
          parent = null;
        }
      } else { // It's not a leaf

        entries[nrElements].element = p.entries[parentIndex].element;
        nrElements++;

        for (int x = nrElements + 1, y = 0; y <= rs.nrElements; x++, y++) {
          entries[x] = rs.entries[y];
          rs.entries[y].child.parent = this;
          nrElements++;
        }
        nrElements--;

        p.entries[++parentIndex].child = this;

        if (p.nrElements == MIN && p != BTreeSet.this.root) {
          for (int x = parentIndex - 1, y = parentIndex - 2; y >= 0; x--, y--)
            p.entries[x] = p.entries[y];
          p.entries[0] = new Entry();
        } else {
          for (int x = parentIndex - 1, y = parentIndex; y <= p.nrElements; x++, y++)
            p.entries[x] = p.entries[y];
          p.entries[p.nrElements] = null;
        }

        p.nrElements--;

        if (p.isRoot() && p.nrElements == 0) { // It's the root and it's empty
          BTreeSet.this.root = this;
          parent = null;
        }
      }
    }
Exemplo n.º 3
0
    /*
     * This method is called only when stealLeft and stealRight could not be called,
     * the BTreeNode has the minimum number of elements, has a leftSibling, and the
     * leftSibling has more than the minimum number of elements.  If after completion
     * parent has fewer than the minimum number of elements than the parents entries[0]
     * slot is left empty in anticipation of a recursive call to stealLeft, stealRight,
     * mergeLeft, or mergeRight to fix the parent. All of the before-mentioned methods
     * expect the parent to be in such a condition.
     */
    private void mergeLeft(int parentIndex) {
      BTreeNode p = parent;
      BTreeNode ls = p.entries[parentIndex - 1].child;

      if (isLeaf()) { // Don't worry about children
        int add = childToInsertAt(p.entries[parentIndex - 1].element, true);
        insertNewElement(
            p.entries[parentIndex - 1].element, add); // Could have been a successor switch
        p.entries[parentIndex - 1].element = null;

        for (int i = nrElements - 1, nr = ls.nrElements; i >= 0; i--) entries[i + nr] = entries[i];

        for (int i = ls.nrElements - 1; i >= 0; i--) {
          entries[i] = ls.entries[i];
          nrElements++;
        }

        if (p.nrElements == MIN && p != BTreeSet.this.root) {

          for (int x = parentIndex - 1, y = parentIndex - 2; y >= 0; x--, y--)
            p.entries[x] = p.entries[y];
          p.entries[0] = new Entry();
          p.entries[0].child =
              ls; // So p doesn't think it's a leaf this will be deleted in the next recursive call
        } else {

          for (int x = parentIndex - 1, y = parentIndex; y <= p.nrElements; x++, y++)
            p.entries[x] = p.entries[y];
          p.entries[p.nrElements] = null;
        }

        p.nrElements--;

        if (p.isRoot() && p.nrElements == 0) { // It's the root and it's empty
          BTreeSet.this.root = this;
          parent = null;
        }
      } else { // I'm not a leaf but fixing the tree structure
        entries[0].element = p.entries[parentIndex - 1].element;
        entries[0].child = ls.entries[ls.nrElements].child;
        nrElements++;

        for (int x = nrElements, nr = ls.nrElements; x >= 0; x--) entries[x + nr] = entries[x];

        for (int x = ls.nrElements - 1; x >= 0; x--) {
          entries[x] = ls.entries[x];
          entries[x].child.parent = this;
          nrElements++;
        }

        if (p.nrElements == MIN && p != BTreeSet.this.root) { // Push everything to the right
          for (int x = parentIndex - 1, y = parentIndex - 2; y >= 0; x++, y++) {
            System.out.println(x + " " + y);
            p.entries[x] = p.entries[y];
          }
          p.entries[0] = new Entry();
        } else { // Either p.nrElements > MIN or p == BTreeSet.this.root so push everything to the
          // left
          for (int x = parentIndex - 1, y = parentIndex; y <= p.nrElements; x++, y++)
            p.entries[x] = p.entries[y];
          p.entries[p.nrElements] = null;
        }

        p.nrElements--;

        if (p.isRoot() && p.nrElements == 0) { // p == BTreeSet.this.root and it's empty
          BTreeSet.this.root = this;
          parent = null;
        }
      }
    }