Sword refers to Offer-57 balanced binary tree

public boolean isBalanced(TreeNode root) {
    return recur(root) != -1;
}

public int recur(TreeNode root) {
    // Follow-up traversal
    if (root == null) {
        return 0;
    }
    int left = recur(root.left);
    if(left == -1) {
        return -1;
    }
    int right = recur(root.right);
    if(right == -1) {
        return -1;
    }
    // If the depth of the left and right subtrees is less than 2, return the depth, otherwise return -1 to determine that it is not balanced
    return Math.abs(left - right) < 2 ? Math.max(left, right) + 1 : -1;
}