add FrogRiverOne

Author: talgat-ruby

README.md

@@ -17,6 +17,7 @@
         -   [TapeEquilibrium](#s_3_tape_equilibrium)
     -   [Lesson 4 - Counting Elements](#s_4)
         -   [PermCheck](#s_4_perm_check)
+        -   [FrogRiverOne](#s_4_frog_river_one)
 -   [Licence](#licence)
 
 <a name="installation"></a>
@@ -143,6 +144,18 @@ https://github.com/talgat-ruby/codility-lessons-javascript/blob/master/lesson4_c
 
 https://app.codility.com/demo/results/trainingCNTYP4-RDE/
 
+<a name="s_4_frog_river_one"></a>
+
+#### FrogRiverOne
+
+##### File
+
+https://github.com/talgat-ruby/codility-lessons-javascript/blob/master/lesson4_counting_elements/FrogRiverOne.js
+
+##### Link to Report
+
+https://app.codility.com/demo/results/training5PWD9F-PE9/
+
 <a name="licence"></a>
 
 ## License

lesson4_counting_elements/FrogRiverOne.js

@@ -0,0 +1,12 @@
+function solution(X, A) {
+    const set = new Set();
+    for (let i = 0; i < A.length; i++) {
+        set.add(A[i]);
+        if (set.size === X) {
+            return i;
+        }
+    }
+    return -1;
+}
+
+module.exports = solution;

lesson4_counting_elements/FrogRiverOne.test.js

@@ -0,0 +1,7 @@
+const solution = require("./FrogRiverOne");
+
+describe("test FrogRiverOne", () => {
+    test("(5, [1, 3, 1, 4, 2, 3, 5, 4]) -> 6", () => {
+        expect(solution(5, [1, 3, 1, 4, 2, 3, 5, 4])).toBe(6);
+    });
+});