Kadane's - Implementation

function maxSubArray(nums)
 maxSum := nums[0]
 currentSum := 0
 for each num in nums
 currentSum := currentSum + num
 if currentSum > maxSum then
 maxSum := currentSum
 if currentSum < 0 then
 currentSum := 0
 return maxSum

Time: $O(n)$. Space: $O(1)$.