0666. Path Sum IV

https://leetcode.com/problems/path-sum-iv

Description

If the depth of a tree is smaller than 5, then this tree can be represented by an array of three-digit integers. For each integer in this array:

• The hundreds digit represents the depth d of this node where 1 <= d <= 4.

• The tens digit represents the position p of this node in the level it belongs to where 1 <= p <= 8. The position is the same as that in a full binary tree.

• The units digit represents the value v of this node where 0 <= v <= 9.

Given an array of ascending three-digit integers nums representing a binary tree with a depth smaller than 5, return the sum of all paths from the root towards the leaves.

It is guaranteed that the given array represents a valid connected binary tree.

Example 1:

**Input:** nums = [113,215,221]
**Output:** 12
**Explanation:** The tree that the list represents is shown.
The path sum is (3 + 5) + (3 + 1) = 12.

Example 2:

**Input:** nums = [113,221]
**Output:** 4
**Explanation:** The tree that the list represents is shown. 
The path sum is (3 + 1) = 4.

Constraints:

• 1 <= nums.length <= 15

• 110 <= nums[i] <= 489

• nums represents a valid binary tree with depth less than 5.

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