404. Sum of Left Leaves

Find the sum of all left leaves in a given binary tree.

Solution1 :Recursive递归，注意：left leaves是左子叶，终端节点才是叶节点。所以只有9和15计算在内

class Solution {

    public int sumOfLeftLeaves(TreeNode root) {

        if (root == null) {

            return 0;

        }

        int ans = 0;

        if (root.left != null) {

            if (root.left.left == null && root.left.right == null)

　　　　　　ans += root.left.val;

            else

　　　　　　ans += sumOfLeftLeaves(root.left);

        }

        ans += sumOfLeftLeaves(root.right);

        return ans;

    }

}

 

 

Solution2：

class Solution {

    public int sumOfLeftLeaves(TreeNode root) {

        if (root == null || root.left == null && root.right == null) {

            return 0;

        }

        int ans = 0;

        Queue<TreeNode> q = new LinkedList<>();

        q.offer(root);

        while (!q.isEmpty()) {

            TreeNode tr = q.poll();

            if (tr.left != null && tr.left.left == null && tr.left.right == null) 

                 ans += tr.left.val;

            if (tr.left != null)

　　　　　　q.offer(tr.left);

            if (tr.right != null)

　　　　　　q.offer(tr.right);

        }

        return ans;

    }

}