Binary Tree Leaf Sum

题目：

Given a binary tree, calculate the sum of leaves.

分析：

简单题，bfs，15分钟

解法：

public class Solution {
    /**
     * @param root the root of the binary tree
     * @return an integer
     */
    public int leafSum(TreeNode root) {
        // Write your code 
        int res = 0;
        if (root == null) {
            return res;
        }

        Queue<TreeNode> myQueue = new LinkedList<TreeNode>();
        myQueue.offer(root);

        while(!myQueue.isEmpty() ) {
            int size = myQueue.size();

            for (int i = 0; i < size; i++) {
                TreeNode temp = myQueue.poll();
                if (temp.left == null && temp.right == null) {
                    res += temp.val;
                    continue;
                }
                if (temp.left != null) {
                    myQueue.offer(temp.left);
                }
                if (temp.right != null) {
                    myQueue.offer(temp.right);
                }
            }
        }
        return res;
    }
}