[LeetCode]16.threeSumClosest

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题目：找出数组中3个数和最接近Target的值
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).
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	int threeSumClosest1(vector<int>& nums, int target)
	{
		if (nums.size() < 3) return 0;
		int closest = nums[0] + nums[1] + nums[2];
		for (int i = 0; i < nums.size()-2; i++)
		{
			int front = i + 1;
			int back = nums.size() - 1;
			while (front < back)
			{
				int Cursum = nums[front] + nums[back]+nums[i];
				if (abs(Cursum - target)<abs(closest - target))
					closest = Cursum;
				if (Cursum == target)
				{
					closest = Cursum;
					return closest;
				}
				if (Cursum>target)
					back--;
				else
					front++;
			}
	    }
		return closest;
	}