LeftLeavesSum.java

public class LeftLeavesSum {

	// Do the inorder traversal
	// check if node if the left child and leaf node
	// if yes then add it to the sum
	public static int leftLeavesSum = 0;

	public static void leftSum(Node root, Node parent) {
		if (root != null) {
			leftSum(root.left, root);
			if (root.left == null && root.right == null && parent.left == root) {
				leftLeavesSum += root.data;
			}
			leftSum(root.right, root);
		}
	}

	public static void main(String args[]) {
		Node root = new Node(10);
		root.left = new Node(5);
		root.right = new Node(15);
		root.left.left = new Node(10);
		root.left.right = new Node(12);
		root.left.right.left = new Node(6);
		root.right.right = new Node(8);
		root.right.right.left = new Node(5);
		leftSum(root, root);
		System.out.println("Sum of left leaves: " + leftLeavesSum);
	}
}

class Node {
	int data;
	Node left;
	Node right;

	public Node(int data) {
		this.data = data;
		this.left = null;
		this.right = null;
	}
}