[LeetCode] 16. 3Sum Closest

最新推荐文章于 2021-08-11 08:50:42 发布

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本文介绍了一种解决3SumClosest问题的有效算法。该问题要求在整数数组中找到三个数，使得这三个数的和最接近给定的目标值。通过先对数组进行排序，然后使用双指针技巧，可以高效地找到最优解。

3Sum Closest

Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.
Example:

Given array nums = [-1, 2, 1, -4], and target = 1.
The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

解析

在数组中找三个数之和，让其与target最相近，返回这个和。
同3Sum的解法，先对数组排序，然后依次固定一个数，再用两个指针遍历后面的数，找到三个数之和最相近的三个数之和。

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int size = nums.size();
        sort(nums.begin(),nums.end());
        int closesum = nums[0]+nums[1]+nums[2];
        int diff = abs(target-closesum);
        for(int i=0;i<size-2;i++){
            int left =i+1,right=size-1;
            while(left<right){
                int sum = nums[i]+nums[left]+nums[right];
                int newdiff = abs(target-sum);
                if(newdiff < diff){
                    closesum = sum;
                    diff = newdiff;
                }
                if(sum < target)
                    left ++;
                else
                    right--;
                    
            }
        }
        return closesum;
    }
};