Subtree of Another Tree

Description

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

     3
    / \
   4   5
  / \
 1   2

Given tree t:

   4 
  / \
 1   2

Return true, because t has the same structure and node values with a subtree of s.

 

Example 2:
Given tree s:

     3
    / \
   4   5
  / \
 1   2
    /
   0

Given tree t:

   4
  / \
 1   2

Return false.

 

Solution(javascript)

const isSubtree = function (s, t) {
  const is = (node1, node2) => {
    if (!node1 && !node2) {
      return true
    }
    if (!node1 || !node2) {
      return false
    }
    if (node1.val !== node2.val) {
      return false
    }
    return is(node1.left, node2.left) && is(node1.right, node2.right)
  }
  const aux = node => is(node, t) || (!!node && aux(node.left, t)) || (!!node && aux(node.right, t))
  return aux(s)
}