Add solution #2657

Author: JoshCrozier

README.md

@@ -431,6 +431,7 @@
 2648|[Generate Fibonacci Sequence](./2648-generate-fibonacci-sequence.js)|Easy|
 2649|[Nested Array Generator](./2649-nested-array-generator.js)|Medium|
 2650|[Design Cancellable Function](./2650-design-cancellable-function.js)|Hard|
+2657|[Find the Prefix Common Array of Two Arrays](./2657-find-the-prefix-common-array-of-two-arrays.js)|Medium|
 2665|[Counter II](./2665-counter-ii.js)|Easy|
 2666|[Allow One Function Call](./2666-allow-one-function-call.js)|Easy|
 2667|[Create Hello World Function](./2667-create-hello-world-function.js)|Easy|

solutions/2657-find-the-prefix-common-array-of-two-arrays.js

@@ -0,0 +1,34 @@
+/**
+ * 2657. Find the Prefix Common Array of Two Arrays
+ * https://leetcode.com/problems/find-the-prefix-common-array-of-two-arrays/
+ * Difficulty: Medium
+ *
+ * You are given two 0-indexed integer permutations A and B of length n.
+ *
+ * A prefix common array of A and B is an array C such that C[i] is equal to the count of
+ * numbers that are present at or before the index i in both A and B.
+ *
+ * Return the prefix common array of A and B.
+ *
+ * A sequence of n integers is called a permutation if it contains all integers from 1 to
+ * n exactly once.
+ */
+
+/**
+ * @param {number[]} A
+ * @param {number[]} B
+ * @return {number[]}
+ */
+var findThePrefixCommonArray = function(A, B) {
+  const result = [];
+
+  for (let i = 0, count = 0, set = new Set(); i < A.length; i++) {
+    if (set.has(A[i])) count++;
+    if (set.has(B[i])) count++;
+    if (A[i] === B[i]) count++;
+    [A[i], B[i]].forEach(n => set.add(n));
+    result.push(count);
+  }
+
+  return result;
+};