[LeetCode] Problem 404 - Sum of Left Leaves

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Find the sum of all left leaves in a given binary tree.

Example

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  3
 / \
9  20
  /  \
 15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

Code

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public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
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public int sumOfLeftLeaves(TreeNode root) {
    if (root == null)
        return 0;
    
    int sum = 0;

    if (root.left != null) {
        if (root.left.left == null && root.left.right == null)
            sum += root.left.val;
        else
            sum += sumOfLeftLeaves(root.left);
    }

    sum += sumOfLeftLeaves(root.right);
    return sum;
}