What I've done today is 10001st prime in Rust and Binary Tree Preorder Traversal in JavaScript.

Math

Problem

10001st prime

Problem 7 

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

What is the 10 001st prime number?

Solution

It's easy to think about use sieve of Eratosthenes to compute prime, whose time complexity is $O(nloglogn)$, or Euler sieve, whose time complexity is $O(n)$.

I'll do it with extern crate. ;)

Implementation

extern crate primal;

fn main() {
    let p = primal::Primes::all().nth(10001 - 1).unwrap();
    println!("The 10001st prime is {}", p);
}

Algorithm

Problem

144. Binary Tree Preorder Traversal

Given a binary tree, return the preorder traversal of its nodes' values.

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,2,3]
Follow up: Recursive solution is trivial, could you do it iteratively?

Solution

;p

Implementation

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var preorderTraversal = (root) => {
  if(root == null) return [];
  let ans = [root.val]
  ans = ans.concat(preorderTraversal(root.left));
  ans = ans.concat(preorderTraversal(root.right));
  return ans;
};

var preorderTraversal = (root) => {
  if(root == null) return [];
  let ans = [root.val];
  let s = [];
  s.push(root.right);
  s.push(root.left);
  while(s.length){
    let tmp = s.pop();
    if(tmp === null) continue;
    ans.push(tmp.val);
    s.push(tmp.right);
    s.push(tmp.left);
  }
  return ans;
};