Compute array of products excluding self (without division) in O(n) time. Efficient two-pass solution using prefix and suffix products; handles zeros and negatives; no division used.

arrayProductExcludingCurrent.ts

// resource of question: https://www.greatfrontend.com/questions/algo/array-product-excluding-current

export default function arrayProductExcludingCurrent(numbers: number[]): number[] {
    const result: number[] = []

    for (let index = numbers.length - 1; index >= 0; index--) {
        result[index] = index === numbers.length - 1 ? 1 : numbers[index + 1] * result[index + 1]// suffix
    }

    let leftProduct = 1
    for (let index = 0; index < numbers.length; index++) {
        leftProduct = index === 0 ? leftProduct : leftProduct * numbers[index - 1]
        result[index] = leftProduct * result[index]
    }

    return result
}
                                               
console.log(arrayProductExcludingCurrent([ 1, 2, 3 ]))
console.log(arrayProductExcludingCurrent([ 2, 0, 3 ]))
console.log(arrayProductExcludingCurrent([ 0, 0, -1, 1 ]))
console.log(arrayProductExcludingCurrent([ 2, 3, 3, 2, 5 ]))// [90, 60, 60, 90, 36]