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
题目含义：给定一个树，判断左右子树是否完全对称
1 private boolean isMirror(TreeNode p,TreeNode q) 2 { 3 if (p==null && q==null) return true; 4 if(p==null || q==null || p.val!=q.val) return false; 5 return isMirror(p.left,q.right) && isMirror(p.right,q.left); 6 } 7 8 public boolean isSymmetric(TreeNode root) { 9 if (root == null) return true; 10 return isMirror(root.left,root.right); 11 }
原文：http://www.cnblogs.com/wzj4858/p/7710794.html