[JavaScript] Graph single cycle check

single-cycle-check.js

const assert = require('assert');

function hasSingleCycle(array) {
  let numberOfVisitedNodes = 0;
  let currentIndex = 0;
  while (numberOfVisitedNodes < array.length) {
    // If we go back to the first element,
    // That shows, we have an infinite loop before our loop ends.
    if (currentIndex === 0 && numberOfVisitedNodes > 0) return false;
    currentIndex = jump(currentIndex, array);
    numberOfVisitedNodes++
  }
  return currentIndex === 0;
}

function jump(currentIndex, array) {
  const nextIndex = (array[currentIndex] + currentIndex) % array.length

  // Cross the other side of array,
  if (nextIndex < 0) {
    return nextIndex + array.length;
  }
  return nextIndex;
}


assert.deepStrictEqual(hasSingleCycle([2, 3, 1, -4, -4, 2]), true)
assert.deepStrictEqual(hasSingleCycle([1, 1, 1, -3]), true)
assert.deepStrictEqual(hasSingleCycle([1, 1, 1, -2]), false)