【leetcode 101】Symmetric Tree 對稱數

題目

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

 

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
   3    3

 解題思路

判斷當前節點值是否一致

判斷當前左節點的左節點值和右節點的右節點值是否一致

判斷當前左節點的右節點值和右節點的左節點值是否一致

代碼實現

    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);
    }