LeetCode 16: 3Sum Closet

Evillla

于 2019-04-27 15:34:16 发布

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分类专栏：剑指Offer和Leetcode

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本文介绍了一种解决三数之和最接近目标问题的算法。通过首先对数组进行排序，然后使用双指针技术，寻找三个数的组合使得其和最接近给定的目标值。算法详细解释了如何遍历数组并调整指针位置以优化解决方案。

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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).

3个数求和系列，基本思路就是先对数组排序，循环一个数，判断另外两个数字的和与 target-第一个数字的差绝对值。

    int threeSumClosest(vector<int>& nums, int target) {
        int n = nums.size();
        if( n < 3)
            return 0;
        sort(nums.begin(),nums.end());
        int min_gap = INT_MAX;
        int _min = 0;
        for(int i = 0;i < n - 2;i++)
        {
            int left = i + 1;
            int right = n - 1;
            int sum = target - nums[i];
            while(left < right)
            {
                if(nums[left] + nums[right] == sum)
                {
                    return target;
                }
                int tmp = nums[i] + nums[left] + nums[right];   
                if(abs(tmp - target) <= min_gap)
                {
                    min_gap = abs(target - tmp);
                    _min = tmp;
                }
                if(nums[left] + nums[right] > sum)
                {
                    right--;
                }
                else
                {
                    left++;
                }
            }
        }
        return _min;
    }