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public class DetectCycle {
	int time;

	public boolean hasCycle(List <Node> nodes) {
		time = 0;

		for (Node node: nodes) {
			if (node.color.equals(Color.White)) {
				if (dfsVisit(node)) {
					return true;

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class Node {
  char c;
  Set <Node> children; 
}

class PrefixGrouper {
  ArrayList <String> result = new ArrayList<String>();
  
  public ArrayList<String> prefixWith(Node root, String prefix) {
    result.clear();

rayjcwu

public boolean isValid(char [][]board) {
  for (int i = 0; i < 9; i++) {
    if (!isValid(board, 0, i, 9, 1) || !isValid(board, i, 0, 1, 9)) {
      return false;
    }
  }
  for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
      if (!isValid(board, 3*i, 3*j, 3, 3)) {
        return false;

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

public String serialize(Node root) {
  StringBuilder sb = new StringBuilder();
  serialize(root, sb);
  return sb.toString();

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class Median {
  MaxHeap maxHeap;
  MinHeap minHeap;
  
  // maintain invariant size of maxHeap equals to or greater than size of minHeap by 1
  public void add(int x) {
    maxHeap.add(x);
    if (maxHeap.size() > minHeap.size() + 1) {
      minHeap.add(maxHeap.remove());
    }

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char unique (String str) {
    HashMap<Character, Integer> map = new HashMap<Character, Integer>();
    Set<Character> set = new SortedHashSet<Character>();
    
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        if (map.containsKey(c)) {
           map.put(c, map.get(c) + 1);
           set.remove(c);
        } else {

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public class StringToLong {
  public long stringToLong(String s) {
    return stringToLong(s, true, true, true);
  }

  public long stringToLong(
      String s,
      boolean allowHeadingTailingSpaces,  // allow spaces in the begin/end of string
      boolean allowNonDigit,        // allow non digit char in the end, will only parse all digits

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import java.util.LinkedList;
import java.util.Queue;

public class TrinaryTree {
  private TrinaryNode root;

  public TrinaryTree insert(int []ary) {
    for (int i: ary) {
      insert(i);
    }

rayjcwu

// first version
float eval(String str) {
  String [] tokens = str.split(" ");
  Stack <Float> stack = new Stack<Float>();

  for (String token: tokens) {
    if (!isOp(token)) {
  } else {
    float right = stack.remove();
    float left = stack.remove();

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public int minCut(String s) {
  final int N = s.length();
  char []str = s.toCharArray();
        
  // build palindrome
  boolean [][] palindrome = new boolean[N][N];
  for (int i = N - 1; i >= 0; --i) {
    for (int j = i; j < N; j++) {
      if (i == j || 
          (str[i] == str[j] && (j - i == 1 || palindrome[i + 1][j - 1]))) {