1191. K-Concatenation Maximum Sum
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Given an integer array arr and an integer k, modify the array by repeating it k times.
For example, if arr = [1, 2] and k = 3 then the modified array will be [1, 2, 1, 2, 1, 2].
Return the maximum sub-array sum in the modified array. Note that the length of the sub-array can be 0 and its sum in that case is 0.
As the answer can be very large, return the answer modulo 109 + 7.
Example 1:
Input: arr = [1,2], k = 3 Output: 9
Example 2:
Input: arr = [1,-2,1], k = 5 Output: 2
Example 3:
Input: arr = [-1,-2], k = 7 Output: 0
Constraints:
1 <= arr.length <= 1051 <= k <= 105-104 <= arr[i] <= 104
Hints
Hint 1
How to solve the problem for k=1 ?
Hint 2
Use Kadane's algorithm for k=1.
Hint 3
What are the possible cases for the answer ?
Hint 4
The answer is the maximum between, the answer for k=1, the sum of the whole array multiplied by k, or the maximum suffix sum plus the maximum prefix sum plus (k-2) multiplied by the whole array sum for k > 1.