404. Sum of Left Leaves
public class Solution {
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;
}
}