238. Product of Array Except Self

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

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up:
Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

 

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example:

given [a0, a1, a2, a3]    => should give [a1a2a3, a0a2a3, a0a1a3, a0a1a2]

　　　　　　　　　　　　 => splits as      [1,            a0,      a0a1, a0a1a2]

　　　　　　　　　　　　　　　　　　*      [a1a2a3,    a2a3,      a3,         1]

 

public class Solution {
   public int[] productExceptSelf(int[] nums) {
    int n = nums.length;
    int[] res = new int[n];
    res[0] = 1;
    for (int i = 1; i < n; i++) {
      res[i] = res[i - 1] * nums[i - 1];
    }
    int right = 1;
    for (int i = n - 1; i >= 0; i--) {
      res[i] *= right;
      right *= nums[i];
    }
    return res;
  }
}