Assuming the problem refers to LeetCode Problem 16: 3Sum Closest, here's the step-by-step solution:
Given an integer array nums and an integer target, find three integers in nums such that their sum is closest to target. Return the sum of these three integers (each input has exactly one solution).
The optimal approach uses sorting + two-pointer technique to reduce the time complexity:
def threeSumClosest(nums, target):
nums.sort()
n = len(nums)
closest_sum = nums[0] + nums[1] + nums[2] # Initial guess
for i in range(n - 2):
left = i + 1
right = n - 1
while left < right:
current_sum = nums[i] + nums[left] + nums[right]
# Update closest sum if current is better
if abs(current_sum - target) < abs(closest_sum - target):
closest_sum = current_sum
# Adjust pointers
if current_sum < target:
left += 1
elif current_sum > target:
right -= 1
else:
return current_sum # Exact match
return closest_sum
O(n log n) time.O(n2) time.O(1) (auxiliary space; sorting uses O(log n) stack space, but it's negligible).For nums = [-1,2,1,-4] and target =1:
[-4,-1,1,2].2 (from triplet -1,1,2), which is 1 unit away from the target.This solution efficiently finds the closest sum and handles all edge cases (like exact matches or all elements being the same).
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