leetcode 238. Product of Array Except Self

Seawolf

1. 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].
   
2. 
   
3. Example:
   
4. 
   
5. Input:  [1,2,3,4]
   
6. Output: [24,12,8,6]
   
7. Note: Please solve it without division and in O(n).
   
8. 
   
9. Follow up:
   
10. Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)

复制代码

1. class Solution {
   
2.     public int[] productExceptSelf(int[] nums) {
   
3.         int mul = 1;
   
4.         int[] res = new int[nums.length];
   
5.         for(int i = 0; i<nums.length; i++){
   
6.             res[i] = 1;
   
7.         }
   
8.         for(int i = 0; i< nums.length; i++){
   
9.             res[i] = res[i] * mul;
   
10.             mul = mul * nums[i];
    
11.          }
    
12.         mul = 1;
    
13.         for(int i = nums.length -1 ; i>=0 ; i--){
    
14.             res[i] = res[i] * mul;
    
15.             mul = mul * nums[i];
    
16.         }
    
17.         
    
18.         return res;
    
19.     }
    
20. }

复制代码