Javascript参考

Question

I'm building out a Binary Search Tree in javascript for some algorithm / data structures practice. I ran into an interesting scenario when implementing delete() , and I'm curious if there is a better way to go about solving this. It really has nothing to do with binary trees, but here are the barebones that you need to know to understand my problem:

function innerDelete(node, parent) {
            switch (node.countChildren(node)) {
                case 0:
                  ...
                case 1:
                    if (node.left)
                        node = node.left;
                    else
                        node = node.right;
                  ...

Props to anyone who can see the problem immediately. This tree is composed of Node objects each with the properties { value, left, right } . This deletion method is updating objects directly so I don't have to manage updating parent references to child nodes. The problem is that reassigning node during node = node.left or node = node.right is only reassigning the local reference to this variable, and not the actual node object. Is there a way to directly update the object itself? Alternatives I've come up with are a little ugly, so I hope there's a better way:

var branch = (parent.left == n ? 'left' : 'right');
if (node.left)
  p[branch] = node.left;
else
  p[branch] = node.right;

Answer 1

The problem is that reassigning node during node = node.left or node = node.right is only reassigning the local reference to this variable, and not the actual node object

That's because the value node is a reference, so it's not that you're changing a local copy of node , you're changing the reference. Therefore, you're not actually changing the object itself.

A cleaner approach for updating trees is to use recursion, with each recursive call updating the left and right nodes as they are returned.

For example:

root = delete(root, target);

function delete(node, target) {
    // Not found
    if (node === null) return null;
    // Found
    if (node.value === target) {
        // If there's children
          // If has both left and right child
            var newNode = minimum(node.right);
            deleteMin(node.right);
            newNode.left = node.left;
            newNode.right = node.right;
            return newNode;  
        // Else
            return null;
    }
    // Update
    node.left = delete(node.left, target);
    node.right = delete(node.right, target);
    return node;
}