1022. Sum of Root to Leaf Binary Numbers

# 1022. Sum of Root To Leaf Binary Numbers#

## 题目 #

You are given the root of a binary tree where each node has a value 0 or 1. Each root-to-leaf path represents a binary number starting with the most significant bit.

For example, if the path is 0 -> 1 -> 1 -> 0 -> 1, then this could represent 01101 in binary, which is 13. For all leaves in the tree, consider the numbers represented by the path from the root to that leaf. Return the sum of these numbers.

The test cases are generated so that the answer fits in a 32-bits integer.

Example 1:

``````Input: root = [1,0,1,0,1,0,1]
Output: 22
Explanation: (100) + (101) + (110) + (111) = 4 + 5 + 6 + 7 = 22
``````

Example 2:

``````Input: root = [0]
Output: 0
``````

Constraints:

• The number of nodes in the tree is in the range `[1, 1000]`.

• `Node.val` is `0` or `1`.

## 解题思路 #

• 当前遍历结点为`nil`，表示本层递归结束了，直接`return 0`

• 如果当前访问结点是叶结点，则返回从根结点到该结点所表示的数值`sum`

• 如果当前访问结点不是叶结点，则返回左子树和右子树所对应的结果之和。

Apr 8, 2023