# LeetCode-Alg-1022-Sum of Root To Leaf Binary Numbers

## LeetCode-Alg-1022-Sum of Root To Leaf Binary Numbers

Posted by Jae on May 20, 2019

### 1、题目

Given a binary tree, each node has 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.

Example 1:

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


Note:

The number of nodes in the tree is between 1 and 1000.
node.val is 0 or 1.
The answer will not exceed 2^31 - 1.


### 3、实现

public class Solution { public int sumRootToLeaf(TreeNode root){ if (root == null){ return 0; }

    return sumRootToLeaf(root, 0);
}
public int sumRootToLeaf(TreeNode root, int val){
int num = val << 1;
num = num | root.val;
// 如果是叶子节点，直接返回此时计算的路径和
if (root.left == null && root.right == null){
return num;
}
int res = 0;
if (root.left != null){
res += sumRootToLeaf(root.left, num);
}
if (root.right != null){
res += sumRootToLeaf(root.right, num);
}
return res;
} }