TinkZhang

class Solution {
  public List<List<Integer>> combine(int n, int k) {
    List<List<Integer>> result = new ArrayList<>();
    Deque<Integer> path = new ArrayDeque<>();
    backtrace(result, 1, path, k, n);
    return result;
  }

  private void backtrace(List<List<Integer>> result, int index, Deque<Integer> path, int k, int n) {
    if(path.size() == k) {

TinkZhang

class Solution {
  public List<List<Integer>> subsetsWithDup(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();
    
    Arrays.sort(nums);
    Deque<Integer> path = new ArrayDeque<>();
    backtrace(result, nums, path, 0);
    return result;
  }

TinkZhang

// Kotlin
class Solution {
  fun kthSmallest(root: TreeNode?, k: Int): Int {
    if(root == null) return 0
    val leftSize = counter(root.left)
    if(leftSize == (k-1)) return root.`val`
    else if(leftSize < (k-1)) return kthSmallest(root.right, k-leftSize-1)
    else return kthSmallest(root.left, k)
  }

TinkZhang

// Kotlin
class Solution {
  fun myPow(x: Double, n: Int): Double {
    if(x == 0.0 || x == 1.0) return x
    return if(n >= 0) 
      quickN(x, n)
      else 
      (1/quickN(x, -(n+1)))/x
  }

TinkZhang

// Kotlin
class Solution {
  fun search(nums: IntArray, target: Int): Int {
    var start = 0
    var end = nums.size - 1
    while(start <= end) {
      val middle = start + (end - start) / 2
      if(nums[middle] == target) return middle
      else if(nums[middle] > target) {
        end = middle - 1

TinkZhang

// Kotlin
class Solution {
  fun searchInsert(nums: IntArray, target: Int): Int {
    var start = 0
    var end = nums.size - 1
    while(start < end) {
      val middle = start + (end - start) / 2
      if(nums[middle] == target) return middle
      else if(nums[middle] > target) {
        end = middle - 1

TinkZhang

// Kotlin
class Solution: VersionControl() {
  override fun firstBadVersion(n: Int) : Int {
    var start = 1
    var end = n
    while(start < end) {
      val middle = start + (end - start) / 2
      if(isBadVersion(middle)) {
        end = middle
      } else {

TinkZhang

// Kotlin
class Solution {
  fun mySqrt(x: Int): Int {
    var start = 1
    var end = x
    while(start <= end) {
      val middle = start + (end - start) / 2
      val temp = middle.toLong() * middle.toLong()
      if(temp > x.toLong()) {
        end = middle - 1

TinkZhang

// Kotlin
class Solution {
  fun characterReplacement(s: String, k: Int): Int {

    var start = 0
    var end = 0
    val counterArray = IntArray(26) { 0 }
    var result = 0
    while(end < s.length) {
      val endChar = s[end]

TinkZhang

// Kotlin
class Solution {
  fun lengthOfLongestSubstring(s: String): Int {
    val set: MutableSet<Char> = mutableSetOf()
    var result = if(s.length == 0) 0 else 1
    var end = -1
    for(start in 0 until s.length) {
      if(start != 0) set.remove(s[start-1])
      while(end + 1 < s.length && !set.contains(s[end+1])) {
        set.add(s[end+1])