Create 027.js

Author: Walker30263

027.js

@@ -0,0 +1,102 @@
+/*
+Define a Quadratic class 
+new Quadratic(a, b, c) to create a quadratic 
+in the form ax^2 + bx + c
+*/
+class Quadratic {
+  constructor(a, b, c) {
+    this.a = a;
+    this.b = b;
+    this.c = c;
+  }
+  
+  //evaluate the quadratic expression at x
+  evaluate(x) {
+    return (this.a*Math.pow(x, 2)) + (this.b*x) + this.c
+  }
+
+
+  //we never have to print the quadratic to solve the problem, so this part is optional
+  //still added it for debugging and progress check purposes
+  toString() {
+    let expression = ``;
+    expression += `${this.a}x^2 `
+    if (this.b > 0) {
+      expression += `+ ${this.b}x `;
+    } else if (this.b < 0) {
+      expression += ` ${this.b}x `;
+    }
+
+    if (this.c > 0) {
+      expression += `+ ${this.c}`;
+    } else if (this.c < 0) {
+      expression += ` ${this.c}`;
+    }
+
+    return expression;
+  }
+}
+
+// check if number n is prime
+function isPrime(n) {
+  if (n < 2) {
+    return null;
+  }
+  
+  for (let i = 2; i < n; i++) {
+    if (n % i === 0) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+// generate array of primes under n
+function genPrimes(n) {
+  let primes = [];
+
+  for (let i = 2; i <= n; i++) {
+    if (isPrime(i)) {
+      primes.push(i);
+    }
+  }
+
+  return primes;
+}
+
+function solution() {
+  let constantTerms = genPrimes(1000); //constant term has to be prime so that the value of the quadratic is a prime when evaluated at 0
+
+  //object to hold quadratic with longest prime number streak for consecutive input values starting at 0
+  //everytime we find a quadratic with a longer streak, we can update this object (line 89)
+  let longestStreak = {
+    quadratic: null,
+    streakLength: 0
+  }
+
+  
+  for (let i = 0; i < constantTerms.length; i++) {
+    for (let b = -1000; b < 1000; b++) {
+      let quadratic = new Quadratic(1, b, constantTerms[i]);
+      
+      let streak = 0;
+      
+      while (isPrime(quadratic.evaluate(streak))) { //while value of polynomial evaluated at n is prime,
+        streak++ //n++
+      }
+
+      if (streak > longestStreak.streakLength) {
+        longestStreak.quadratic = quadratic;
+        longestStreak.streakLength = streak;
+        console.log(`Just checked ${quadratic.toString()}, streak length of ${streak}`); //progress check, print the quadratic everytime one with the longest prime number streak so far is found
+      }
+    }
+  }
+
+
+  //log the product of the coefficient of the linear term and the constant term (the answer that the question's asking for)
+  console.log(longestStreak.quadratic.b * longestStreak.quadratic.c);
+}
+
+solution();