Tree:给定二叉树与一个定值，判断从根节点到叶子节点是否存在一

public static boolean hasPathSum(BinTreeNode root, int sum) {
        if(root == null) return false;
        if(root.left == null && root.right == null && sum - root.value == 0) return true;
        return hasPathSum(root.left, sum - root.value) || hasPathSum(root.right, sum - root.value);
    }