238. Product of Array Except Self

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題目敘述

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]

解題思路

Solution

class Solution {
    public int[] productExceptSelf(int[] nums) {
        int n = nums.length;
        int[] prefixSum = new int[n];
        int[] suffixSum = new int[n];
        int[] res = new int[n];

        prefixSum[0] = 1;
        suffixSum[n - 1] = 1;
        for(int i = 0; i < n - 1; i++){
            prefixSum[i + 1] = prefixSum[i] * nums[i];
            suffixSum[n - i - 2] = suffixSum[n - i - 1] * nums[n - i - 1];
        }

        for(int i = 0; i < n; i++){
            res[i] = prefixSum[i] * suffixSum[i];
        }

        return res;
    }
}