LeetCode 1022. 从根到叶的二进制数之和(Sum of Root To Leaf Binary Numbers)

1022. 从根到叶的二进制数之和
1022. Sum of Root To Leaf Binary Numbers

题目描述
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.

LeetCode1022. Sum of Root To Leaf Binary Numbers

Example 1:

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

Note:

1. The number of nodes in the tree is between 1 and 1000. 2. node.val is 0 or 1. 3. The answer will not exceed 2^31 - 1.

Java 实现

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

class Solution {
    public int sumRootToLeaf(TreeNode root) {
        return def(root, 0);
    }

    public int def(TreeNode root, int sum) {
        if (root == null) {
            return 0;
        }
        sum = 2 * sum + root.val;
        if (root.left == null && root.right == null) {
            return sum;
        }
        int leftSum = root.left == null ? 0 : def(root.left, sum);
        int rightSum = root.right == null ? 0 : def(root.right, sum);
        return leftSum + rightSum;
    }
}

参考资料