LintCode 1360 · Symmetric Tree.java

Binary Search:
note that: "Check the left.left equal to the right.right."

	/**
	* Definition of TreeNode:
	* public class TreeNode {
	* public int val;
	* public TreeNode left, right;
	* public TreeNode(int val) {
	* this.val = val;
	* this.left = this.right = null;
	* }
	* }
	*/
	// Approach #1 - Recursion - T O(#OfNodes).
	public class Solution {
	/**
	* @param root: root of the given tree
	* @return: whether it is a mirror of itself
	*/
	public boolean isSymmetric(TreeNode root) {
	// Write your code here
	if (root == null) {
	return true;
	}
	return isSymmetric(root.left, root.right);
	}
	private boolean isSymmetric(TreeNode left, TreeNode right) {
	if (left == null && right == null) {
	return true;
	}
	if (left == null || right == null) {
	return false;
	}
	return isSymmetric(left.left, right.right) && isSymmetric(left.right, right.left);
	}
	}

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