###### tags: `Weekly Contest`
# Weekly Contest 358

## [2815. Max Pair Sum in an Array](https://leetcode.com/problems/max-pair-sum-in-an-array) (<font color=#00B8A3>Easy</font>)

限制 :

<ul>
<li><code>2 <= nums.length <= 100</code></li>
<li><code>1 <= nums[i] <= 10^4</code></li>
</ul>

### Solution
注意題意是講說，數字的最大位一樣。這樣就可以很簡單解出來了。

#### 時間複雜度: $O(n^2)$

#### 空間複雜度: $O(1)$

程式碼:

class Solution {
public:
    bool isPair(int num1, int num2)
    {
        int max1 = 0, max2 = 0;
        while(num1>0)
        {
            max1 = max(max1, num1%10);
            num1/=10;
        }
        while(num2>0)
        {
            max2 = max(max2, num2%10);
            num2/=10;
        }
        if(max1==max2) return true;
        return false;

    }

    int maxSum(vector<int>& nums) {
        int result = -1;
        for(int i=0; i< nums.size() - 1;i++)
        {
            for(int j = i + 1; j < nums.size(); j++)
            {
                if(isPair(nums[i], nums[j]) == true)
                {
                    result = max(result, nums[i] + nums[j]);
                }
            }
        }
        return result;
    }
};

## [2816. Double a Number Represented as a Linked List](https://leetcode.com/problems/double-a-number-represented-as-a-linked-list) (<font color=#FFC011>Medium</font>)

限制 :

<ul>
<li><code>The number of nodes in the list is in the range [1, 104]</code></li>
<li><code>0 <= Node.val <= 9</code></li>
<li><code>The input is generated such that the list represents a number that does not have leading zeros, except the number 0 itself.</code></li>
</ul>

### Solution
這題不算難，因為只有乘2，所以最多只會進一位，這樣就是用兩個指標，這兩個指標都會在相鄰位置，在右邊的負責把裡面的數字相乘，如果要進位，會請左邊指標的值加一。
#### 時間複雜度: $O(n)$

#### 空間複雜度: $O(1)$

程式碼:

class Solution {
public:
    ListNode* doubleIt(ListNode* head) {

        if (head->val >= 5) {
            ListNode* temp = new ListNode();
            temp->next = head;
            head = temp;
        } else {
            head->val = head->val * 2;
        }
        ListNode* curr = head;
        ListNode* r = curr->next;
        while (r != nullptr) {
            if (r->val >= 5) {
                curr->val += 1;
                r->val = r->val * 2 - 10;
            } else {
                r->val *= 2;
            }
            r = r->next;
            curr = curr->next;
        }
        return head;
    }
};

## [2817. Minimum Absolute Difference Between Elements With Constraint](https://leetcode.com/problems/minimum-absolute-difference-between-elements-with-constraint)(<font color=#FFC011>Medium</font>)

限制 :

<ul>
<li><code>10⁴</code></li>
</ul>
### Solution

#### 時間複雜度: $O()$

#### 空間複雜度: $O()$

程式碼:

## [2818. Apply Operations to Maximize Score](https://leetcode.com/problems/apply-operations-to-maximize-score)(<font color=#FF375F>Hard</font>)

限制 :

<ul>
<li><code>10⁴</code></li>
</ul>
### Solution

#### 時間複雜度: $O()$

#### 空間複雜度: $O()$

程式碼: