Create 2040-kth-smallest-product-of-two-sorted-arrays.js

Author: everthis

2040-kth-smallest-product-of-two-sorted-arrays.js

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+/**
+ * @param {number[]} nums1
+ * @param {number[]} nums2
+ * @param {number} k
+ * @return {number}
+ */
+const kthSmallestProduct = function(nums1, nums2, k) {
+  const neg = nums1.filter(e => e < 0)  
+  const pos = nums1.filter(e => e >= 0)
+  const negRev = neg.slice(), posRev = pos.slice()
+  negRev.reverse()
+  posRev.reverse()
+
+  let l = - (10 ** 10), r = 10 ** 10
+  while(l < r) {
+    const mid = l + Math.floor((r - l) / 2)
+    if(fn(mid) < k) l = mid + 1
+    else r = mid
+  } 
+
+  return l
+
+  function fn(val) {
+    let res = 0, n = nums2.length
+    let l = 0, r = n - 1
+    const list = val >= 0 ? negRev.concat(pos) : neg.concat(posRev)
+    for(let e of list) {
+      if(e < 0) {
+        while(l < n && e * nums2[l] > val) l++
+        res += n - l
+      } else if (e === 0) {
+        if(val >= 0) res += n
+      } else {
+        while(r >= 0 && e * nums2[r] > val) r--
+        res += r + 1
+      }
+    }
+    return res
+  }
+};