res.js

/**
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number}
 */
var findMedianSortedArrays = function(nums1, nums2) {
  const len1 = nums1.length;
  const len2 = nums2.length;

  let left = (len1 + len2 + 1) >> 1;
  let right = (len1 + len2 + 2) >> 1;

  const getMedian = (n1, s1, e1, n2, s2, e2, k) => {
    const l1 = e1-s1+1;
    const l2 = e2-s2+1;

    if (l1 > l2) return getMedian(n2, s2, e2, n1, s1, e1, k);
    if (l1 === 0) return n2[s2+k-1];

    if (k == 1) return Math.min(n1[s1], n2[s2]);

    let i = s1 + Math.min(l1, k >> 1) - 1;
    let j = s2 + Math.min(l2, k >> 1) - 1;

    if (n1[i] > n2[j]) {
      return getMedian(n1, s1, e1, n2, j+1, e2, k - (j-s2+1));
    } else {
      return getMedian(n1, i+1, e1, n2, s2, e2, k - (i-s1+1));      
    }
  }

  return (getMedian(nums1, 0, len1-1, nums2, 0, len2-1, left) + getMedian(nums1, 0, len1-1, nums2, 0, len2-1, right)) / 2;
};