Split array largest sum

We binary search largest sum in range [max(nums), sum(nums)], which is left = max(nums), right = sum(nums).

• mid = left + (right - left) // 2
• If canPartition(mid) then:
  • Update the answer so far then try to minimize the largest sum by right = mid - 1
• Else:
  • Increate the largest sum by left = mid + 1.
• We need to write function canPartition(largestSum) to check if we can divide nums array into m subarrays such that no subarray sum is greater than largestSum.
  • We greedily take as many as elements to form a subarray as long as the sum of each subarray <= largestSum.
  • And check if we can form k subarray, with k <= m.

class Solution:
    def splitArray(self, nums: List[int], k: int) -> int:
        def canPartition(largestSum):
            groups = 1
            curSum = 0
            for num in nums:
                curSum += num
                if curSum > largestSum:
                    groups += 1
                    curSum = num
            return groups <= k

        left, right = max(nums), sum(nums)
        res = right
        while left <= right:
            mid = left+(right-left)//2
            if canPartition(mid):
                res = mid
                right = mid-1
            else:
                left = mid+1
        return res