LeetCode 16. 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).

题解: 首先将数组排序，固定一个数字， 设定两个指针，当这3个数的和大于target的时候，第二个指针往前移动，当小于target的时候，第一个指针往后移动，知道两个指针指向相同的值或者是三个数的和等于target。

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int closest = nums[0] + nums[1] + nums[2];
        unsigned int diff = abs(target - closest);
        sort(nums.begin(), nums.end());
        int length = nums.size();
        for (int i = 0; i < length - 2; ++i)
        {
            int j = i + 1;
            int k = length - 1;
            while (j != k && diff != 0)
            {
                int tempSum = nums[i] + nums[j] + nums[k];
                unsigned int tempDiff = abs(target - tempSum);
                if (tempDiff < diff)
                {
                    diff = tempDiff;
                    closest = tempSum;
                }
                if (tempSum > target)
                {
                    --k;  //前移第二个指针
                }
                if (tempSum < target)
                {
                    ++j;  //后移第一个指针
                }
            }
            if (diff == 0)
                break;
        }
        return closest;
    }
};