Leetcode 16. 3Sum Closest

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).

这一题和3Sum解法差不多，而且还更简单，因为不用考虑去重的问题。首先排序nums。 然后只要for loop 一下k, 并考虑[i, j]。 每次碰到一个更接近的，就更新一下res。需要注意的是如果current sum = target, 跳出即可。如果cur sum > target, j --，反之 i++.

class Solution(object):
    def threeSumClosest(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        n = len(nums)
        nums.sort()
        res = nums[0] + nums[1] + nums[2]
 
        for i in range(n):
            j = i + 1
            k = n - 1
            while j < k:
                sum = nums[i] + nums[j] + nums[k]
 
                if abs(sum - target) < abs(res - target):
                    res = sum
 
                if sum == target:
                    return sum
                elif sum > target:
                    k -= 1
                else:
                    j += 1
 
        return res