Coprimes up to N

54d3bb4dfc75996c1c000c6d/index.js

@@ -0,0 +1,21 @@
+
+const midpointSum = arr => {
+  const sums = [];
+  let sum = 0;
+  sums[-1] = 0;
+  for (let i = 0; i < arr.length; ++i) {
+    sums[i] = arr[i] + sums[i-1];
+    sum += arr[i];
+  }
+  for (let i = 1; i < arr.length - 1; ++i) {
+    if (sums[i-1] === sum - sums[i]) {
+      return i;
+    }
+  }
+  return null;
+};
+
+midpointSum([-10,3,7,8,-6,-13,21]);
+midpointSum([0,0,4,0]);
+midpointSum([9,0,1,2,3,4]);
+midpointSum([4, 1, 7, 9, 3, 9]);

59e0dbb72a7acc3610000017/index.js

@@ -0,0 +1,33 @@
+
+const getGCD = ZERO => {
+  return (a, b) => {
+    if (a < ZERO) a = -a;
+    if (b < ZERO) b = -b;
+    if (b > a) {
+      [a, b] = [b, a];
+    }
+    while (true) {
+      if (b === ZERO) return a;
+      a %= b;
+      if (a === ZERO) return b;
+      b %= a;
+    }
+  };
+};
+
+const gcd = getGCD(0);
+const gcdBI = getGCD(0n);
+
+const coprimes = n => {
+  return new Array(n).fill(0).map((_, i) => i + 1).filter(i => {
+    return gcd(n, i) === 1;
+  });
+};
+
+coprimes(2); // -> [1]
+coprimes(3); // -> [1, 2]
+coprimes(6); // -> [1, 5]
+coprimes(10); // -> [1, 3, 7, 9]
+coprimes(20); // -> [1, 3, 7, 9, 11, 13, 17, 19]
+coprimes(25); // -> [1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19, 21, 22, 23, 24]
+coprimes(30); // -> [1, 7, 11, 13, 17, 19, 23, 29]