leetcode-3 sum 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).

思路：与3sum类似，排序，先固定其中一个；

     判断sum与target的距离distance，距离越小，则更新结果res。

     如果sum<target，++p，p指针右移，否则，--q,q指针左移。

代码：

int threeSumClosest(vector<int> &num,int target)
{
int res;
int dist;
int mindist=0xffff;


int len=num.size();
if(len<3)
{
return 0;
}
sort(num.begin(),num.end());


for(int i=0;i<len-2;++i)
{
if(i!=0 && num[i]==num[i-1])
{
continue;
}

int p=i+1;
int q=len-1;
while(p<q)
{
dist=target>(num[i]+num[p]+num[q])?(target-num[i]-num[p]-num[q]):(num[i]+num[p]+num[q]-target);


if(mindist>dist)
{
mindist=dist;
res=num[i]+num[p]+num[q];
}
if(mindist==0)
{
return res;
}
if(target>(num[i]+num[p]+num[q]))
{
++p;
}
else if(target<(num[i]+num[p]+num[q]))
{
--q;
}
}
}
return res;
}