LeetCode 16. 3Sum Closest (预处理排序)

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).

这个也是预处理排序，不过和15题不同的是它不需要跳过相同的数字，这两个数相加也是OK的。

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int diff = 1 << 30;    //初始设一个很大的数
        sort(nums.begin(), nums.end());
        int begin;
        int back = (int)nums.size() - 1;
        int cloestNum;
        
        for(begin = 0; begin < back; begin ++){
            int front = begin + 1;
            back = (int)nums.size() - 1;
            while(front < back){
                if(fabs(nums[begin] + nums[front] + nums[back]  - target) < diff){
                    cloestNum = nums[front] + nums[back] + nums[begin];
                    diff = fabs(cloestNum - target);
                }
                if(diff == 0)
                    return target;
                
                if(nums[front] + nums[back] + nums[begin] > target )
                    back --;
                else
                    front ++;
            }
            
            while(begin+1 < back && nums[begin] == nums[begin + 1])
                begin++;
        }
        return cloestNum;
    }
};