Binary Tree Pruning

Description

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

Example 1:
Input: [1,null,0,0,1]
Output: [1,null,0,null,1]
Explanation:
Only the red nodes satisfy the property "every subtree not containing a 1".
The diagram on the right represents the answer.

Example 2:
Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]

Example 3:
Input: [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]

Note:

• The binary tree will have at most 200 nodes.
• The value of each node will only be 0 or 1.

Solution(javascript)

const pruneTree = function (root) {
  const hasOne = (node) => {
    if (!node) {
      return [null, false]
    }
    const [left, leftValid] = hasOne(node.left)
    const [right, rightValid] = hasOne(node.right)
    const valid = node.val === 1 || leftValid || rightValid
    node.left = left
    node.right = right
    return valid ? [node, true] : [null, false]
  }
  return hasOne(root)[0]
}