238. Product of Array Except Sel

除自身以外数组元素的乘积。先求出整个数组的乘积，再除以当前元素，需要考虑0的个数。或将某个位置上的元素的乘积，等于左边的元素积乘以右边元素的乘积。

• Runtime: 120 ms, faster than 70.15%
• Memory Usage: 48.9 MB, less than 77.30%

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var productExceptSelf = function(nums) {
    let len = nums.length
    if(len === 0) return []
    let triple = 1
    let zero = 0
    for(let i = 0; i < len; i++) {
        if(nums[i]) {
            triple *= nums[i]
        } else {
            zero++
        }
    }
    let res = Array(len).fill(0)
    if(zero === 1) {
        let index = nums.indexOf(0)
        res[index] = triple
    } else if(zero === 0) {
        for(let i = 0; i < len; i++) {
            res[i] = triple / nums[i]
        }
    }
    return res
};