Solution404.java

package binary_search_tree_problem;

public class Solution404 {

    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }

    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) {
            return 0;
        }
        if (isLeaf(root.left)) {
            return root.left.val + sumOfLeftLeaves(root.right);
        }
        return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
    }

    private boolean isLeaf(TreeNode node) {
        if (node == null) {
            return false;
        }
        return node.left == null && node.right == null;
    }

}