Similar to 3Sum, we sort the array and use Two Pointers. Instead of looking for exactly 0, we track the sum with the minimum absolute difference from the target.

1. Sort nums.
2. best_sum = float('inf').
3. For i in range(len(nums)):
   • l = i + 1, r = len(nums) - 1.
   • While l < r:
     • curr_sum = nums[i] + nums[l] + nums[r].
     • If abs(target - curr_sum) < abs(target - best_sum): best_sum = curr_sum.
     • If curr_sum < target, l += 1.
     • Else if curr_sum > target, r -= 1.
     • Else, return target.
4. Return best_sum.

• Time Complexity: O(N^2).
• Space Complexity: O(log N) to O(N).

def three_sum_closest(nums, target):
    nums.sort()
    res = nums[0] + nums[1] + nums[2]
    
    for i in range(len(nums)):
        l, r = i + 1, len(nums) - 1
        while l < r:
            s = nums[i] + nums[l] + nums[r]
            if abs(s - target) < abs(res - target):
                res = s
            if s > target:
                r -= 1
            elif s < target:
                l += 1
            else:
                return res
    return res