0404. Sum of Left Leaves #

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        int ans = 0;
        while (queue.size() != 0) {
            int k = queue.size();
            for (int i = 0; i < k; i++) {
                TreeNode node = queue.poll();
                if (node.left != null) {
                    queue.offer(node.left);
                    if (node.left.left == null && node.left.right == null) ans += node.left.val;
                }
                if (node.right != null) {
                    queue.offer(node.right);
                }
            }
        }
        return ans;
    }
}