running sum

running_sum.go

// O(n) time, O(n) space
func runningSum(nums []int) []int {
    if len(nums) <= 1 { return nums }
    
    var result []int // O(n) space complexity
    result = append(result, nums[0])
    for i := 1; i < len(nums); i++ { // O(n) time complexity
        result = append(result, nums[i]+(result[i-1]))
    }
    return result
}

// O(n) time, O(1) space
func runningSum(nums []int) []int {
    if len(nums) <= 1 { return nums }
    
    runSum := nums[0]
    
    for i := 1; i < len(nums); i++ { // O(n) time complexity
        nums[i-1] = runSum
        runSum += nums[i]
    }
    nums[len(nums)-1] = runSum
    
    return nums
}