114.flatten-binary-tree-to-linked-list.kt

/*
 * @lc app=leetcode id=114 lang=kotlin
 *
 * [114] Flatten Binary Tree to Linked List
 *
 * https://leetcode.com/problems/flatten-binary-tree-to-linked-list/description/
 *
 * algorithms
 * Medium (48.29%)
 * Likes:    2761
 * Dislikes: 330
 * Total Accepted:    345.7K
 * Total Submissions: 708.9K
 * Testcase Example:  '[1,2,5,3,4,null,6]'
 *
 * Given a binary tree, flatten it to a linked list in-place.
 * 
 * For example, given the following tree:
 * 
 * 
 * ⁠   1
 * ⁠  / \
 * ⁠ 2   5
 * ⁠/ \   \
 * 3   4   6
 * 
 * 
 * The flattened tree should look like:
 * 
 * 
 * 1
 * ⁠\
 * ⁠ 2
 * ⁠  \
 * ⁠   3
 * ⁠    \
 * ⁠     4
 * ⁠      \
 * ⁠       5
 * ⁠        \
 * ⁠         6
 * 
 * 
 */

// @lc code=start
/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun flatten(root: TreeNode?): Unit {
        var cur = root

        while (cur != null) {
            if (cur?.left != null) {
                var p = cur?.left
                while (p?.right != null) {
                    p = p?.right
                }
                p?.right = cur?.right
                cur?.right = cur?.left
                cur?.left = null
            }
            cur = cur?.right
        }
    }
}
// @lc code=end