16. 3Sum Closest

Leetcode

Given an array $S$ of $n$ integers, find three integers in $S$ such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

For example, given array S = {-1 2 1 -4}, and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

这道题目和前面的3Sum问题差不多，主要是改变了target值，只要在寻找target的过程中，不断更新最接近于target的值就可以了。

import sys

class Solution:
    def threeSumClosest(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        n = len(nums)

        # 考虑特殊情况
        if n < 3:
            return []

        nums = sorted(nums)
        print(nums)

        i = 0
        approx_target = sys.maxsize
        while i < n-2:
            left = i + 1
            right = n - 1
            while (left < right):
                val = nums[i] + nums[left] + nums[right]
                if val == target:
                    return target
                elif abs(val-target) < abs(approx_target-target):
                        approx_target = val
                elif val < target:
                    left += 1
                else:
                    right -= 1

            i += 1

        return approx_target

Runtime: 136 ms, beats 97.28 %