1. Two Sum

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function (nums, target) {
  const idx = new Map()
  for (let i = 0; i < nums.length; i++) {
    v = nums[i]
    t = target - v
    if (idx.has(t)) {
      return [idx.get(t), i]
    }
    idx.set(v, i)
  }
}