前序遍历:根结点->左结点->右结点 对称前序遍历:根结点->右结点->左结点 比较前序遍历 and 对称前序遍历的序列判断二叉树是否是对称的。
/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class SymmetricalBinaryTree {
boolean isSymmetrical(TreeNode pRoot)
{
return isSymmetrical(pRoot, pRoot);
}
boolean isSymmetrical(TreeNode root1, TreeNode root2) {
if(root1 == null && root2 == null) {
return true;
} else if(root1 != null && root2 != null) {
return (root1.val == root2.val) && isSymmetrical(root1.left, root2.right) && isSymmetrical(root1.right, root2.left);
} else {
return false;
}
}
}