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给定一个整型数组和key，找三个数，使其和与key最相近，返回这三个数的和。（假设至少会有一个解）
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).
相似题：3Sum
考虑特殊情况：
采用twoSum的双指针法，只需额外维护一个最近的三个数和即可。
public class Solution { public int threeSumClosest( int[] nums, int target ){ int len = nums.length; if( len<3 ) return 0; Arrays.sort( nums ); int closestThree = nums[0] + nums[1] + nums[2]; for( int i=0; i<len-2; i++ ){ //use two pointers find the closest two for i for( int j=i+1, k=len-1; j<k; ){ int nowThree = nums[i] + nums[j] + nums[k]; int distance = target - nowThree; //update j & k if( distance < 0 ) k--; else if( distance > 0 ) j++; //find the exact three integers that sum to target else return target; //update closestThree if( Math.abs( distance) < Math.abs( target - closestThree)) closestThree = nowThree; } } return closestThree; } }
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原文地址：http://www.cnblogs.com/hf-cherish/p/4607017.html
