```
public class Solution {
public boolean isBalanced(TreeNode root) {
// 1:20pm - 1:33pm
return height(root) != -1;
}
private int height(TreeNode root) {
if (root == null) {
return 0;
}
int leftHeight = height(root.left);
if (leftHeight == -1) {
return -1;
}
int rightHeight = height(root.right);
if (rightHeight == -1) {
return -1;
}
if (Math.abs(leftHeight - rightHeight) > 1) {
return -1;
}
return 1 + Math.max(leftHeight, rightHeight);
}
}
```