Create 786-k-th-smallest-prime-fraction.js

Author: everthis

786-k-th-smallest-prime-fraction.js

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+/**
+ * @param {number[]} A
+ * @param {number} K
+ * @return {number[]}
+ */
+const kthSmallestPrimeFraction = function(A, K) {
+  let ans = []
+  let left = 0.0
+  let right = 1.0
+  while (right - left > 1e-9) {
+    const mid = left + (right - left) / 2
+    const { count, p, q } = maxUnder(mid, A)
+    if (count >= K) {
+      ans = [p, q]
+      right = mid
+    } else {
+      left = mid
+    }
+  }
+  return ans
+
+  function maxUnder(x, primes) {
+    let [p, q] = [0, 1]
+    let count = 0
+    let l = -1
+    for (let r = 1; r < primes.length; r++) {
+      while (primes[l + 1] < primes[r] * x) {
+        l += 1
+      }
+      count += l + 1
+      if (l >= 0 && p * primes[r] < q * primes[l]) {
+        ;[p, q] = [primes[l], primes[r]]
+      }
+    }
+    return { count, p, q }
+  }
+}