Product of array except self

productOfArrayExceptSelf.js

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var productExceptSelf = function(nums) {
    let prefix = 1;
    let postfix = 1;
    let res = [];
    for(let i=0; i<nums.length; i++) {
        res[i] = prefix;
        prefix = prefix * nums[i];
    }

    for(let i=nums.length - 1; i>=0; i--) {
        res[i] = res[i] * postfix;
        postfix = postfix * nums[i];
    }

    return res;
};

// run a loop to calculate prefix product and add them to the result array 
// run another loop from behind and calculate postfix and multiply it with the current stored prefix