Two-Sum O(n) soltuion

 1 class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        N = len(nums)
        l, r = 0, N-1
        while l < r:
            s = nums[l] + nums[r]
            if s < target:
                l += 1
            elif s > target:
                r -= 1
            else: # s == target
                return l+1, r+1
        return None