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class Main {
  public static void main(String[] args) {
    System.out.println("Hello world!");
  }
}

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// Problem 1290: Convert Binary Number in a Linked List to Integer
// Link: https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer
// Solution 1: using an array to store the values, multiply each value by its bit later
func getDecimalValue(_ head: ListNode?) -> Int {
    if head == nil { return 0 }

    var headCopy = head
    // an array stores all the values
    var vals = [Int]()
    var bit = 1

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */

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// Problem 69. Sqrt(x)
//Link: https://leetcode.com/problems/sqrtx/submissions/
// Solution: Binary seearch
// Time: O(logn), Space: O(1)
class Solution {
    public int mySqrt(int x) {
        if (x < 2) { return x; }
        
        long left = 0;
        long right = x / 2 + 1;

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// Problem 118. Pascal's Triangle
// Link: https://leetcode.com/problems/pascals-triangle/
// Solution: An element = one above + one before above
// Time: O(n^2), Space: O(n^2)
public List<List<Integer>> generate(int numRows) {
    List<List<Integer>> result = new ArrayList<List<Integer>>();
    if (numRows == 0) { return result; }

    result.add(new ArrayList<>(Arrays.asList(1)));

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// Problem 938. Range Sum of BST
// Link: https://leetcode.com/problems/range-sum-of-bst/
// Solution: Depth first search recursive
// Time: O(n), Space: O(n) TODO why?
var sum = 0
func rangeSumBST(_ root: TreeNode?, _ L: Int, _ R: Int) -> Int {
    dfs(root, L, R)
    return sum
}

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// 700. Search in a Binary Search Tree
// link: https://leetcode.com/problems/search-in-a-binary-search-tree/
// Solution: recursive
// Time O(n), Space O(n)
public TreeNode searchBST(TreeNode root, int val) {
    if (root == null) { return null; }
    if (root.val == val) { return root; }

    TreeNode node = root.val < val 
                    ? searchBST(root.right, val)

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// Time O(n), Space O(1)
func hasConsecutiveOdds(_ nums: [Int]) -> Bool {
    var oddCount = 0
    var index = 0
    
    while index != nums.count
    {
        if nums[index] % 2 == 1 {
            oddCount += 1
            if oddCount == 3 { return true }

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// 5. Longest Palindromic Substring
// Link: https://leetcode.com/problems/longest-palindromic-substring/
// Time O(n^2), Space O(1)
var maxLength = 0
var firstIndex = 0
func longestPalindrome(_ s: String) -> String {

    if s.count < 2 { return s }
    let sArray = Array(s)
    for i in 0..<sArray.count-1 {

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// 238. Product of Array Except Self
// Link: https://leetcode.com/problems/product-of-array-except-self/
func productExceptSelf(_ nums: [Int]) -> [Int] {
      let count = nums.count
      var result = Array(repeating: 1, count: count)

      for i in 1..<count {
          result[i] = result[i - 1] * nums[i - 1]
      }