[LeetCode]016-3Sum-Closest

题目：
3Sum 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).

Solution:
解法就是上一题思路的延伸。
1、先排序
2、求和，与target比较
3、找出相距最小的和

  int threeSumClosest(vector<int>& nums, int target)     {        int i,j,k;        int n = nums.size();        if(n<3)            return 0;        int min_value = abs(nums[0]+nums[1]+nums[2] - target);        int result = nums[0]+nums[1]+nums[2];        QuickSort(nums,0,n-1);        for(i=0;i<n;i++)        {            int current_num = nums[i];            j = i+1;            k = n-1;            while(j<k)            {                int sum  = nums[j] + nums[k] + current_num;                if(sum - target < 0)                {                    j++;                }                else if(sum - target > 0)                {                    k--;                }                else                {                    result = sum;                    return result;                }                if(abs(sum-target) < min_value)                {                    min_value = abs(sum-target);                    result = sum;                }            }        }        return result;    }    void QuickSort(vector<int>& nums,int low,int high)    {        if(low<high)        {            int pivot = nums[low];            int first = low;            int last = high;            while(first<last)            {                while(nums[last] >= pivot && first <last)                {                    last--;                }                nums[first] = nums[last];                while(nums[first] < pivot && first <last)                {                    first++;                }                nums[last] = nums[first];            }            nums[first] = pivot;            QuickSort(nums,low,first-1);            QuickSort(nums,first+1,high);        }        else            return;    }