LeetCode 016 3Sum Closest

题目

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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).

给一组数和一个目标数，找到其中3个数，这3个数满足条件相加与目标数最接近。输出这样的三个数之和。

思路

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和之前的3sum方法一样 http://blog.csdn.net/xift810/article/details/19175113

有些细节要变化一下：

a 需要有个差值记录器，每当差距缩小的时候，都要记录下来。

b 当3个数总和相同时候，直接输出答案。

c 最开始的差值用系统最大值。

代码

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 public int threeSumClosest(int[] num, int target) {        if(num==null|| num.length<3){return 0;}Arrays.sort(num);int len = num.length;int leaf = Integer.MAX_VALUE;int ans=target;for(int i=0;i<len-2;i++){if(i>0&&num[i]==num[i-1]){continue;}int l = i +1;int r = len-1;while(l<r){int sum= num[i] + num[l] + num[r];if (Math.abs(sum-target)<leaf) {  leaf=Math.abs(sum-target);ans = sum;}if(sum==target){return target;}else if(sum < target){do{l++;}while(l<r&&num[l-1]==num[l]);}else{do{r--;}while(l<r&&num[r]==num[r+1]);}}}return ans;    }

15.3.1.8 注意  

if(sum==target){return target;}