PassingCars.md

PassingCars

Count the number of passing cars on the road.

Solution (JavaScript)

In this challenge we can keep track of the number of cars travelling east, then every time we pass a car travelling west we know that each car going east will make another pairs.

Test Score: 100%

function solution(A) {
    let east = 0
    let pairs = 0
    
    for (let i = 0; i < A.length; ++i) {
        if (A[i] === 0) east++
        else {
            pairs += east
            // if we exceed the passing car count then return
            if (pairs > 1000000000) return -1
        }
    }
    
    return pairs
}