Question

我正在尝试用Java构建一个AVL树，但是我在旋转后更新高度时遇到了麻烦。这是我遇到问题的代码。

 public void checkHeights(Node<T> u) {
  if (u == nil) return;
  checkHeights(u.left);
  checkHeights(u.right);
  System.out.println(u.h);
  if (height(u) != 1 + Math.max(height(u.left), height(u.right)))
   throw new RuntimeException("Check heights shows incorrect heights");
  int dif = height(u.left) - height(u.right);
  if (dif < -1 || dif > 1)
   throw new RuntimeException("Check heights found height difference of " + dif);
 }

 /**
  * Fix up
  * @param u
  */
 public void fixup(Node<T> u) {
  while (u != nil) {
   int dif = height(u.left) - height(u.right);
   if(debug)System.out.println("Node dif at " + u.x + " is: " + dif);
   if (dif > 1) {
     if(debug)System.out.println("u.left is larger");
     if(height(u.left.left) - height(u.left.right) < 0) {
       if(debug)System.out.println("u.left dif is: " + (height(u.left.left) - height(u.left.right)));
       rotateLeft(u.left);
     }
     rotateRight(u);

   } else if (dif < -1) {
     if(debug)System.out.println("u.right is larger");
     if(height(u.right.left) - height(u.right.right) > 0) {
       if(debug)System.out.println("u.right dif is: " + (height(u.right.left) - height(u.right.right)));
       rotateRight(u.right);
     }
     rotateLeft(u);
   }
   if(debug) System.out.println("Height of " + u.x + " is " + height(u));
   u = u.parent;
  }
 }

 public void rotateLeft(Node<T> u) {
  super.rotateLeft(u);
  u.h = Math.max(height(u.left), height(u.right)) + 1;
  u.parent.h = Math.max(height(u.parent.left), height(u.parent.right)) + 1;
  if(debug)System.out.println("After left rotation, " + u.x + " has height " + u.h + " and " + u.parent.x + " has height " + u.parent.h);
 }

 public void rotateRight(Node<T> u) {
  super.rotateRight(u);
  u.h = Math.max(height(u.left), height(u.right)) + 1;
  u.parent.h = Math.max(height(u.parent.left), height(u.parent.right)) + 1;
  if(debug)System.out.println("After right rotation, " + u.x + " has height " + u.h + " and " + u.parent.x + " has height " + u.parent.h);
 }

我已经完成了一系列单元测试，并且我一直在让checkHeights抛出异常。我几乎肯定发生的事情是当旋转发生在大于2的深度时，高度不会递归地更新到树上。例如，如果我添加从0到10的值，则第一个左旋转没有问题，并且值得到正确的高度，但是当我尝试向下旋转时，父节点不能准确地更新到它们的新高度，导致异常被抛出。

非常感谢任何帮助

Java AVL树问题

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