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.)
sdf
前几天刚看facebook的面经出现这题, leetocde就加上了, 不能用除法, 则维护当前元素左边所有元素的乘积以及右边所有元素的乘积, 相乘得到 product of array except self !
Because we cannot use division, so assume we have two integer arrays with the same length of nums, int[] leftProd = new int[nums.length]; int[] rightProd = new int[nums.length]
, we store the product of all the left elements in leftProd
and the product of all the right elements in rightProd
, then the product of leftProd[i]
and rightProd[i]
will be the value we want to put into the result. take the example of num[] = {2, 4, 3, 6}
, thenleftProd
will be {1, 2, 8, 24}
, and rightProd will be {72, 18, 6, 1}
.
public class Solution {
public int[] productExceptSelf(int[] nums) {
if(nums == null)
return null;
int[] res = new int[nums.length];
for(int i = 0; i < nums.length; i++){
if(i == 0)
res[i] = 1;
else
res[i] = res[i - 1] * nums[i - 1];
}
int prod = 1;
for(int i = nums.length - 1; i >= 0; i--){
res[i] = res[i] * prod;
prod *= nums[i];
}
return res;
}
}