Sum of Left Leaves
Easy
Given the root of a binary tree, calculate the sum of all left leaves in the tree. A leaf is a node with no children. A left leaf is a leaf that is the left child of its parent.
Example 1
Input
[ [ 3, 9, 20, null, null, 15, 7 ] ]
Output
24
Explanation. The left leaf of the tree is the node with value 9 and the left leaf of the node 20 is 15. Thus, the sum is 9 + 15 = 24.
Example 2
Input
[ [ 1 ] ]
Output
0
Explanation. The tree only has one node, which is not a leaf.
Example 3
Input
[ [ 1, 2 ] ]
Output
2
Explanation. The node with value 2 is a left leaf.
Follow-up: Could you solve it both recursively and iteratively?
Constraints:
The tree can have from 1 to 100 nodes. Each node's value will be a non-negative integer.
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