leetcode 3Sum Closest

和之前的3Sum一樣，隻是等于0換成了求最小差距，  加個cha即可，記得是絕對值！

int threeSumClosest(vector<int>& nums, int target) 
{
  int i,n,ans,left,right,num1,num2,num3,sum,cha;
  n=nums.size();
  sort(nums.begin(),nums.end());
  ans=99999999;
  for(i=0;i<n;i++)
  {
    num1=nums[i];
    left=i+1;
    right=n-1;
    while(left<right)
    {
      num2=nums[left];
      num3=nums[right];
      sum=num1+num2+num3;
      if(sum-target>0)
        right--;
      else if(sum-target<0)
        left++;
      else if(sum-target==0)
        return sum;

      cha=sum-target;
      if(abs(cha)<abs(ans))
        ans=cha;
    }
  }
  return ans+target;
        
}