16 3sum closest

def threeSumClosest(self, nums, target):
        nums.sort()
        global_closest_diff,global_sum = math.inf,0
        for first in range(len(nums)-2):
            second,third = first + 1,len(nums)-1
            if first - 1 >= 0 and nums[first] == nums[first-1]:
                continue
            while second < third:
                threesum = nums[first] + nums[second] + nums[third]
                if threesum >= target:
                    while second < third and nums[first]+nums[second]+nums[third] >= target: #advance third to find turning point !
                        if threesum == target:
                            return target
                        third -= 1
                    if abs(nums[first]+nums[second]+nums[third+1]-target) < global_closest_diff:
                        global_sum = nums[first]+nums[second]+nums[third+1]
                        global_closest_diff = abs(nums[first]+nums[second]+nums[third+1]-target)
                else:
                    while second < third and nums[first]+nums[second]+nums[third] < target: #advance second to find turning point !
                        second += 1
                    if abs(nums[first]+nums[second-1]+nums[third]-target) < global_closest_diff:
                        global_sum = nums[first]+nums[second-1]+nums[third]
                        global_closest_diff = abs(nums[first]+nums[second-1]+nums[third]-target)
        return global_sum