leetcode007-3Sum Closest

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).

解题思路：

类似3Sum的解题，先排序，每次固定下第i个位置的元素，然后在第i个位置后的元素中利用左右指针找到当中距离target距离最小的包含第i个元素的三元素组合。再从这些局部最佳的组合中，找到最佳的那个。

以下是AC的代码

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