Choose three non-overlapping contiguous subarrays of nums, each of length k, so that the sum of all chosen values is as large as possible. Return their three starting indices in increasing order. If several choices have the same maximum sum, return the lexicographically smallest index list: prefer the smaller first index, then the smaller second index, then the smaller third index.
Example 1:
Input: nums = [4,1,5,1,6]
k = 1
Output: [0,2,4]Explanation: With length 1, choose the values 4, 5, and 6 at indices 0, 2, and 4. Their total is 15, the largest sum of three available values.
Example 2:
Input: nums = [2,2,2,2,2,2,2]
k = 2
Output: [0,2,4]Explanation: Every length-2 subarray sums to 4, so every valid choice has total 12. The earliest possible non-overlapping starts are [0, 2, 4], which is the lexicographically smallest answer.
Example 3:
Input: nums = [1,9,8,1,7,6]
k = 2
Output: [0,2,4]Explanation: The array has exactly six values, so three length-2 subarrays must cover it completely. Their starts are 0, 2, and 4, giving sums 10, 9, and 13.
Constraints:
3 <= nums.length <= 200001 <= nums[i] <= 655351 <= k <= floor(nums.length / 3)