Leetcode解题-3Sum Closest

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描述

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).

和上一题3Sum基本设定一样，不过这次要求找到与target最相近的三数之和。返回和的值即可，不需要给出所有组合。

分析

沿用3Sum的解法，用一个变量维护当前最小绝对差值即可。时间复杂度O(n^2)，空间复杂度O(1)。

代码

Python

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class Solution:
    def threeSumClosest(self, nums, target):
        nums.sort()
        ret = None
        cur_diff = None
        for i in xrange(len(nums) - 2):
            j = i + 1
            k = len(nums) - 1
            while j < k:
                s = nums[i] + nums[j] + nums[k]
                if s == target:
                    return target
                elif s > target:
                    k -= 1
                else:
                    j += 1
                if cur_diff is None or cur_diff > abs(s - target):
                    cur_diff = abs(s - target)
                    ret = s
        return ret

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