3Sum Closest

最新推荐文章于 2020-09-08 11:56:16 发布

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本文介绍了一个算法问题——寻找数组中三个整数的组合，使其和最接近给定的目标值，并提供了一段C++代码实现。通过先排序再使用双指针技巧，该算法能在O(n²)的时间复杂度内解决问题。

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).

Code:

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target)
{
	sort(num.begin(),num.end());
	int ret=0;
	int flags=false;
	for(int i=0;i<num.size();i++)
	{
		int j=i+1;
		int k=num.size()-1;
		while(j<k)
		{
			int sum=num[i]+num[j]+num[k];
			if(!flags)
			{
				ret=sum;
				flags=true;
			}
			else
			{
				if(abs(sum-target)<abs(ret-target))
				{
					ret=sum;
				}
			}
			if(target==ret)
				return ret;
			else if(target<sum)
				k--;
			else
				j++;
		}	
	}
	return ret;
}
};