404

404. Sum of Left Leaves (Easy)

Given the root of a binary tree, return the sum of all left leaves.

 

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 24
Explanation: There are two left leaves in the binary tree, with values 9 and 15 respectively.

Example 2:

Input: root = [1]
Output: 0

 

Constraints:

• The number of nodes in the tree is in the range [1, 1000].
• -1000 <= Node.val <= 1000

Companies:
Apple, Adobe, Amazon

Related Topics:
Tree, Depth-First Search, Breadth-First Search, Binary Tree

Solution 1. DFS

// OJ: https://leetcode.com/problems/sum-of-left-leaves
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(H)
class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root, bool isLeft = false) {
        if (!root) return 0;
        if (!root->left && !root->right) return isLeft ? root->val : 0;
        return sumOfLeftLeaves(root->left, true) + sumOfLeftLeaves(root->right);
    }
};