nanjingdaqi

public class Node {
  int val;
  Node left;
  Node right;
}

public void inOrderScan(Node root) {
  if (root == null) return;
  
  Node cur = root;

nanjingdaqi

public class Node {
  int val;
  Node left;
  Node right;
}

public void preOrderScan(Node root) {
  if (root == null) return;
  
  Stack s = new Stack();

nanjingdaqi

public int parent(int i) {
  return (i-1)/2;
}

public int left(int i) {
  return i*2+1;
}

public int right(int i) {
  return left(i)+1;

nanjingdaqi

public void quickSort(int[] arr) {
  if (arr == null || arr.length <= 1) return;
  
  quickSort(arr, 0, arr.length);
}

public void quickSort(int[] arr, int s, int e) {
  if (arr.length == 0 || s >= e) return;
  
  int sepIndex = partition(arr, s, e);

nanjingdaqi

public class Node {
  int val;
  Node next;
}

public Node reverseList(Node head) {
  if (head == null || head.next == null) {
    return head;
  }
  

nanjingdaqi

public class Sig {
  
  private static volatile Sig sInstance;
  
  private Sig() {
  }
  
  public static Sig getInstance() {
    if (sInstance == null) {
      synchronized(Sig.class) {