# Product of Array Except Self

```python
class Solution:
    def productExceptSelf(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        """
        Input:  [1,2,3,4]
        Output: [24,12,8,6]
        
        24 = 2 * 3 * 4
        12 = 1 * 3 * 4
        此題不能用除法
        
        [a, b,   c,         d]
         | /|  / |
        [1 1*a 1*a*b  1*a*b*c ]
        再倒著回來做一遍即可得到答案
        """
        p = 1
        res = []
        for i in range(0, len(nums)):
            output.append(p)
            p = p * nums[i]
        p = 1
        for i in range(n-1,-1,-1):
            output[i] = output[i] * p
            p = p * nums[i]
        return res
```


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