leetcode 016 —— 3Sum Closest

最新推荐文章于 2020-06-30 10:35:22 发布

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最新推荐文章于 2020-06-30 10:35:22 发布

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分类专栏：算法学习数据结构

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本文介绍了一种算法，用于在给定数组中找到三个数，使得它们的和与给定的目标数之间的差距最小。通过贪心算法实现，确保找到最优解。

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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：设定closest，closest与target差值最小，类似贪心算法

class Solution {
public:
	int threeSumClosest(vector<int>& nums, int target) {
		int n = nums.size();
		if (n < 3) return 0;
		int closest = nums[0]+nums[1]+nums[2];
		sort(nums.begin(), nums.end());
		for (int i = 0; i < n-2; i++){
			if (i>0 && nums[i] == nums[i - 1])
				continue;
			int l = i + 1;
			int r = n - 1;
			while (l < r){
				int sum = nums[i] + nums[l] + nums[r];
				if (sum == target)
					return sum;
				else if(sum>target){
					closest = (abs(closest - target) < abs(sum - target) ? closest : sum);
					r--;					
				}
				else{
					closest = (abs(closest - target) < abs(sum - target) ? closest : sum);
					l++;
				}
			}
		}
		return closest;
	}
};