LeetCode 1822. Sign of the Product of an Array 解題紀錄

Elvire included in leetcode

2021-12-20 254 words One minute

Contents

題目

Problem

There is a function signFunc(x) that returns:

1 if x is positive.
-1 if x is negative.
0 if x is equal to 0. You are given an integer array nums. Let product be the product of all values in the array nums.

Return signFunc(product).

Example 1:

Input: nums = [-1,-2,-3,-4,3,2,1]
Output: 1

Explanation: The product of all values in the array is 144, and signFunc(144) = 1

Example 2:

Input: nums = [1,5,0,2,-3]
Output: 0

Explanation: The product of all values in the array is 0, and signFunc(0) = 0

Example 3:

Input: nums = [-1,1,-1,1,-1]
Output: -1

Explanation: The product of all values in the array is -1, and signFunc(-1) = -1

Constraints:

1 $\leq$ nums.length $\leq$ 1000
-100 $\leq$ nums[i] $\leq$ 100

想法

當 nums 中有任何元素為 0，乘積必為 0；會造成結果 +1 與 -1 擺盪，只與數字前的正負號有關，所以可以忽略數值的運算。

解法

int arraySign(vector<int>& nums) {

    auto ans = 1;

    for(auto i:nums)
    {
        // 只有 nums 中有元素為 0，乘積必為 0
        if(i == 0)  return 0;

        // 若這個元素為負值，必定會造成結果乘以 (-1)
        if(i<0)
        {
            ans = (-1) * ans;
        }
    }

    return ans;
}

Time complexity: $\mathcal{O}(n)$.
Space complexity: $\mathcal{O}(1)$.