Java中二叉树元素的求和

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) {
        this.val = val;
    }
}

public class BinaryTreeSum {
    public int sum(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftSum = sum(root.left);
        int rightSum = sum(root.right);
        return root.val + leftSum + rightSum;
    }

    public static void main(String[] args) {
        // 构建一个二叉树
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);

        BinaryTreeSum binaryTreeSum = new BinaryTreeSum();
        int sum = binaryTreeSum.sum(root);
        System.out.println("二叉树元素的和为：" + sum);
    }
}