0979. Distribute Coins in Binary Tree

https://leetcode.com/problems/distribute-coins-in-binary-tree

Description

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.

Example 3:

**Input:** root = [1,0,2]
**Output:** 2

Example 4:

**Input:** root = [1,0,0,null,3]
**Output:** 4

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.

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