238. Product of Array Except Self

Given an array nums of n integers where n > 1,  return an array output
such that output[i] is equal to the product of all the elements of nums except nums[i].

Example:

Input:  [1,2,3,4]
Output: [24,12,8,6]

Two Pass

public int[] productExceptSelf(int[] nums) {
    int[] result = new int[nums.length];
    int product = 1;
    for(int i = 0; i < nums.length; i++) {
        result[i] = product;
        product *= nums[i];
    }
    product = 1;
    for(int i = nums.length-1; i >= 0; i--) {
        result[i] *= product;
        product *= nums[i];
    }
    return result;
}

Two Pass More Space

public int[] productExceptSelfBad(int[] nums) {
    if(nums.length == 0) return new int[0];
    int[] left = new int[nums.length], right = new int[nums.length];
    left[0] = 1;
    right[nums.length-1] = 1;
    for(int i = 1; i < nums.length; i++) left[i] = left[i-1] * nums[i-1];
    for(int i = nums.length-2; i >= 0; i--) right[i] = right[i+1] * nums[i+1];
    int[] result = new int[nums.length];
    for(int i = 0; i < result.length; i++) result[i] = left[i] * right[i];
    return result;
}