101_Symmetric_tree

// https://leetcode.com/problems/symmetric-tree

// Solution 1

public boolean isSymmetric(TreeNode root) {
    return isMirror(root, root);
}

public boolean isMirror(TreeNode t1, TreeNode t2) {
    if (t1 == null && t2 == null) return true;
    if (t1 == null || t2 == null) return false;
    return (t1.val == t2.val)
        && isMirror(t1.right, t2.left)
        && isMirror(t1.left, t2.right);
}

// Solution 2

public boolean isSymmetric(TreeNode root) {
    Queue<TreeNode> q = new LinkedList<>();
    q.add(root);
    q.add(root);
    while (!q.isEmpty()) {
        TreeNode t1 = q.poll();
        TreeNode t2 = q.poll();
        if (t1 == null && t2 == null) continue;
        if (t1 == null || t2 == null) return false;
        if (t1.val != t2.val) return false;
        q.add(t1.left);
        q.add(t2.right);
        q.add(t1.right);
        q.add(t2.left);
    }
    return true;
}

// My approach(Fail)
public boolean isSymmetric(TreeNode root){
  inorder(root);
  return isPalindrome();
  }
public void inorder(TreeNode root){
        if(root!=null)
        {inorder(root.left);
        arr.add(root.val);
        inorder(root.right);}
    }
    public boolean isPalindrome()
    {
        int start = 0;
        int end = arr.size()-1;
        while(start!=end)
        {
            if(arr.get(start)!=arr.get(end))
                return false;
            start++;
            end--;
        }
        return true;
    }
}