Jocelyn9

class Solution {
    TreeNode a = null, b = null, pre = null;
	public void recoverTree(TreeNode root) {
		if (root == null)
			return;

		recover(root);
		TreeNode temp = new TreeNode(0);
		temp.val = a.val;
		a.val = b.val;

Jocelyn9

/* Time complexity O(nlogn), Space complexity O(1)  */

class Solution1{
  
  boolean isPerm(String s1, String s2){
    if(s1==null||s2==null) return false;
    if(s1.length()!=s2.length()) return false;
    char[] arr1 = s1.toCharArray();
    char[] arr2 = s2.toCharArray();
    Arrays.sort(arr1);

Jocelyn9

/*Solution 1: 
  Brute force.
  Complexity: O(n^2)
  Space complexity O(1)
*/

public class Solution1{
  boolean isUnique(String str){
    // boundary condition
    if(str==null||str=="") return true;