LeetCode-in-All
238. Product of Array Except Self
Medium
Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].
The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
You must write an algorithm that runs in O(n) time and without using the division operation.
Example 1:
Input: nums = [1,2,3,4]
Output: [24,12,8,6]
Example 2:
Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]
Constraints:
2 <= nums.length <= 105-30 <= nums[i] <= 30- The product of any prefix or suffix of
numsis guaranteed to fit in a 32-bit integer.
Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Solution
class Solution {
func productExceptSelf(_ nums: [Int]) -> [Int] {
var res = Array(repeating: 1, count: nums.count)
var pre = 1
for i in 0..<nums.count {
res[i] *= pre
pre *= nums[i]
}
var post = 1
for i in (0..<nums.count).reversed() {
res[i] *= post
post *= nums[i]
}
return res
}
}