39.leetcode16_3sum_cloest

1.题目描述

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.

在数组S中找到三个数字的和最接近目标数字，返回这个和的值

    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).

2.题目分析

先将数组排序。然后先固定一个元素，然后双指针分别从头尾遍历。遇见和等于目标数字的直接返回目标数字，否则继续遍历，找到最接近目标数字的值。

3.解题思路

class Solution(object):
    def threeSumClosest(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        temp=2**31-1 #给temp一个最大值
        nums.sort() #nums列表排序
        l=len(nums)
        i=0
        while i<l-2:   
            left=i+1
            right=l-1
            while left<right:
                sum=nums[i]+nums[left]+nums[right]
                if sum==target: #sum与target相等，返回target
                    return target
                else:
                    if abs(sum-target)<abs(temp-target): #如果当前sum更接近目标数字，temp为当前sum
                        temp=sum
                    if sum-target>0: #如果sum比目标数字大，右指针移动
                        right-=1
                    else: #否则左指针移动
                        left+=1
            i+=1
        return temp