Cars Passing

A non-empty zero-indexed array A consisting of N integers is given. The consecutive elements of array A represent consecutive cars on a road.The goal is to count passing cars. We say that a pair of cars (P, Q), where 0 ≤ P < Q < N, is passing when P is traveling to the east and Q is traveling to the west.

Example:
console.log(PassingCars([0,1,0,1,1])); -> 5

function PassingCars(inputArray) {
  let suffixSum = new Array(inputArray.length + 1).fill(0);
  let count = 0;

for (let i = inputArray.length - 1; i >= 0; i--) {
  suffixSum[i] = inputArray[i] + suffixSum[i + 1];
  if (inputArray[i] === 0) count += suffixSum[i];
  if (count > 1000000000) return -1;
}

return count;
}

console.log(PassingCars([0,1,0,1,1])); -> 5

We create a function called CarsPassing with parameter called inputArray we create an variable called suffixSum and it will be an array with size of inputArray.length + 1 and initially we fill the array with 0. Next we create varible count that we initialize to 0;

We create for loop where we start with i = inputArray.length - 1, second condition is i is bigger or equal to 0 and third condition is where we decrement i by 1;

The way we compute the suffixSum is to write suffixSum[i] = inputArray[i] + suffixSum[i + 1]; suffixSum one position more than i and i + 1 is the reason why we have created the suffixSum to be one position bigger than our inputs.

And in this way the suffix sum area is kindd of a table containing the numbers of cars that are still in front of us for each position.

Next we have if statement if (inputArray[i] === 0) count += suffixSum[i] Meaning that the car is traveling EAST we need to update the count variable with count += suffixSum[i]

Final thing we have to do is another if statement if (count > 1000000000) return -1; If the count is bigger than 1,000,000,000 we return -1;


In the end we return count;