[Swift Weekly Contest 127]LeetCode1005. K 次取反后最大化的数组和 | Maximize Sum Of Array After K Negations

Given an array A of integers,we must modify the array in the following way: we choose an i and replace A[i] with -A[i],and we repeat this process K times in total.  (We may choose the same index i multiple times.)

Return the largest possible sum of the array after modifying it in this way. 

Example 1:

Input: A = [4,2,3],K = 1 Output: 5 Explanation: Choose indices (1,) and A becomes [4,-2,3]. 

Example 2:

Input: A = [3,-1,2],K = 3 Output: 6 Explanation: Choose indices (1,2) and A becomes [3,1,2]. 

Example 3:

Input: A = [2,-3,5,-4],K = 2 Output: 13 Explanation: Choose indices (1,4) and A becomes [2,3,4]. 

Note:

1. 1 <= A.length <= 10000
2. 1 <= K <= 10000
3. -100 <= A[i] <= 100

给定一个整数数组 A，我们只能用以下方法修改该数组：我们选择某个个索引 i 并将 A[i] 替换为 -A[i]，然后总共重复这个过程 K 次。（我们可以多次选择同一个索引 i。）

以这种方式修改数组后，返回数组可能的最大和。 

示例 1：

输入：A = [4,K = 1
输出：5
解释：选择索引 (1,) ，然后 A 变为 [4,3]。

示例 2：

输入：A = [3,K = 3
输出：6
解释：选择索引 (1,2) ，然后 A 变为 [3,2]。

示例 3：

输入：A = [2,K = 2
输出：13
解释：选择索引 (1,4) ，然后 A 变为 [2,4]。 

提示：

1. 1 <= A.length <= 10000
2. 1 <= K <= 10000
3. -100 <= A[i] <= 100

Runtime: 44 ms

Memory Usage: 19.1 MB

 1 class Solution {
 2     func largestSumAfterKNegations(_ A: [Int],_ K: Int) -> Int {
 3         var A = A
 4         var K = K
 5         A.sort()
 6         for i in 0..<A.count
 7         {
 8             if K > 0 && A[i] < 0
 9             {
10                 A[i] = -A[i]
11                 K -= 1                
12             }
13         }
14         A.sort()
15         if K % 2 == 1
16         {
17             A[0] = -A[0]
18         }
19         var ret:Int = 0
20         for a in A
21         {
22            ret += a 
23         }
24         return ret
25     }
26 }