Add solution #786

Author: JoshCrozier

Diff for: README.md

@@ -596,6 +596,7 @@
 783|[Minimum Distance Between BST Nodes](./0783-minimum-distance-between-bst-nodes.js)|Easy|
 784|[Letter Case Permutation](./0784-letter-case-permutation.js)|Medium|
 785|[Is Graph Bipartite?](./0785-is-graph-bipartite.js)|Medium|
+786|[K-th Smallest Prime Fraction](./0786-k-th-smallest-prime-fraction.js)|Medium|
 790|[Domino and Tromino Tiling](./0790-domino-and-tromino-tiling.js)|Medium|
 791|[Custom Sort String](./0791-custom-sort-string.js)|Medium|
 796|[Rotate String](./0796-rotate-string.js)|Easy|

Diff for: solutions/0786-k-th-smallest-prime-fraction.js

@@ -0,0 +1,53 @@
+/**
+ * 786. K-th Smallest Prime Fraction
+ * https://leetcode.com/problems/k-th-smallest-prime-fraction/
+ * Difficulty: Medium
+ *
+ * You are given a sorted integer array arr containing 1 and prime numbers, where all the integers
+ * of arr are unique. You are also given an integer k.
+ *
+ * For every i and j where 0 <= i < j < arr.length, we consider the fraction arr[i] / arr[j].
+ *
+ * Return the kth smallest fraction considered. Return your answer as an array of integers of size
+ * 2, where answer[0] == arr[i] and answer[1] == arr[j].
+ */
+
+/**
+ * @param {number[]} arr
+ * @param {number} k
+ * @return {number[]}
+ */
+var kthSmallestPrimeFraction = function(arr, k) {
+  const n = arr.length;
+  let left = 0;
+  let right = 1;
+
+  while (left < right) {
+    const mid = (left + right) / 2;
+    let count = 0;
+    let maxFraction = [0, 1];
+    let j = 1;
+
+    for (let i = 0; i < n - 1; i++) {
+      while (j < n && arr[i] > mid * arr[j]) {
+        j++;
+      }
+
+      count += n - j;
+
+      if (j < n && arr[i] * maxFraction[1] > maxFraction[0] * arr[j]) {
+        maxFraction = [arr[i], arr[j]];
+      }
+    }
+
+    if (count === k) {
+      return maxFraction;
+    } else if (count < k) {
+      left = mid;
+    } else {
+      right = mid;
+    }
+  }
+
+  return [];
+};