PathSum.kt

/**
 * Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
 *
 * For example:
 * Given the below binary tree and sum = 22,
 *
 * 5
 * / \
 * 4  8
 * /  / \
 * 11 13 4
 * /  \   \
 * 7  2   1
 * return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
 *
 * Accepted.
 */
class PathSum {

    fun hasPathSum(root: TreeNode?, sum: Int): Boolean = root != null && (root.left == null && root.right == null && sum == root.`val` || hasPathSum(root.left, sum - root.`val`) || hasPathSum(root.right, sum - root.`val`))

    data class TreeNode(
            var `val`: Int,
            var left: TreeNode? = null,
            var right: TreeNode? = null
    )

}