Add javaScript solution to Beginner-POPGATES

Author: Mr0cket

Beginner/At the Gates (POPGATES)/gates.js

@@ -0,0 +1,50 @@
+//initalise testCase#s - t from process input.
+// Test case engine clearly uses old NodeJS stdin stream mode. 
+// Assume from js solutions to other tasks:  Stdin is initially paused. must call .resume() to resume stream.
+// process.stdin.resume();
+// process.stdin.setEncoding("utf8");
+// Assume: readline is supported
+const rl = require('readline').createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+// t # of test cases: number , n array containing number of coins in test case, k array containing number of ops
+// coins array of arrays containing coin states for each testcase.
+let t, nArr = [], kArr = [], coinStatesArr = [];
+// assign variables
+const variable = {
+    lineCount : 1,
+    getVars(input) {
+        if (this.lineCount === 1) {t = parseInt(input); // initialise t once.
+        } else if(this.lineCount % 3 === 0) {
+            let line = input.split(' ')
+            coinStatesArr[this.lineCount / 3 - 1] = line.map(coin => coin === 'H' ? true : false); //remap coin values => H = true, T = false or easier flipping
+        } else if (this.lineCount % 2 === 0) {
+            let line = input.split(' ');
+            nArr[this.lineCount / 2 - 1] = line[0]
+            kArr[this.lineCount / 2 - 1] = line[1]
+        }
+        this.lineCount ++
+    }
+};
+// assume: synchronous process.stdin
+rl.on('line', variable.getVars)
+rl.resume()
+// Get variables in order. 
+
+let nHeads
+for (let i = 0; i<t; i++) {
+    coinStates = coinStatesArr[i]
+    n = nArr[i] - 1 // -1 to align to 0 start index.
+    k = kArr[i]
+    for (let j = 0; j<k; j++) {
+        // if last value of coinStates === true, remove last value & flip all coin states.
+        if (coinsStates[n]) {
+            coinStates.pop(); // remove last value of coinstates
+            coinsStates.map(coinState => coinState ? false : true); // flip coin states true <=> false.
+        } else coinstates.pop();
+    }
+    nHeads = 0; //reinitialise nheads after each loop
+    coinstates.forEach(state => state ? nHeads ++ : null);
+    console.log(nHeads); //output nHeads
+}