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# Symmetric Tree?

Check if given tree is symmetrical

**Solution:** Bottom up recursion

**Base Case:**

1. Both null return true
2. One null return false
3. Left key != right key return false

**Implementation:**

```
public boolean isSymmetricHelper(TreeNode left, TreeNode right){
    if (left == null && right == null) return true;
    else if (left == null || right == null) return false;
    else if(left.key != right.key) return false;

    return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left);
  }
```

**Time Comp:** O(N) Every node visited

**Space Comp:** O(Height) max stack size