LeetCode in Kotlin

979. Distribute Coins in Binary Tree

Medium

You are given the root of a binary tree with n nodes where each node in the tree has node.val coins. There are n coins in total throughout the whole tree.

In one move, we may choose two adjacent nodes and move one coin from one node to another. A move may be from parent to child, or from child to parent.

Return the minimum number of moves required to make every node have exactly one coin.

Example 1:

Input: root = [3,0,0]

Output: 2

Explanation: From the root of the tree, we move one coin to its left child, and one coin to its right child.

Example 2:

Input: root = [0,3,0]

Output: 3

Explanation: From the left child of the root, we move two coins to the root [taking two moves]. Then, we move one coin from the root of the tree to the right child.

Constraints:

• The number of nodes in the tree is n.
• 1 <= n <= 100
• 0 <= Node.val <= n
• The sum of all Node.val is n.

Solution

import com_github_leetcode.TreeNode
import kotlin.math.abs

/*
 * 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 {
    private var num = 0
    fun distributeCoins(root: TreeNode?): Int {
        helper(root)
        return num
    }

    private fun helper(node: TreeNode?): Int {
        if (node == null) {
            return 0
        }
        val total: Int = node.`val` + helper(node.left) + helper(node.right)
        val leftover = total - 1
        num += abs(leftover)
        return leftover
    }
}

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