[LeetCode][Python]16: 3Sum Closest

# -*- coding: utf8 -*-‘‘‘__author__ = ‘[email protected]‘

16: 3Sum Closesthttps://oj.leetcode.com/problems/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).

===Comments by Dabay===先排序，然后从左到右固定一个数，在后边的数列中使用左右指针往中间靠拢的方法查找。当比之前更接近target的时候，更新找个这个值。

从左往右固定一个数,左右两个指针往中间靠拢。‘‘‘class Solution:    # @return an integer    def threeSumClosest(self, num, target):        if len(num) < 3:            return []        num.sort()        closest = num[0] + num[1] + num[2]        difference = abs(target - closest)        for i in xrange(len(num)-2):            j, k = i+1, len(num)-1            while j < k:                sum = num[i] + num[j] + num[k]                if abs(target - sum) < difference:                    closest = sum                    difference = abs(target - sum)                if sum == target:                    return sum                elif sum < target:                    j = j + 1                else:                    k = k - 1        return closest

def main():    sol = Solution()    nums = [-3,0,1,2]    solution = sol.threeSumClosest(nums, 1)    print solution

if __name__ == "__main__":    import time    start = time.clock()    main()    print "%s sec" % (time.clock() - start)