[Leetcode]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).

先將所有元素排序，然後再遍歷所有組合。

class Solution {
public:
	int threeSumClosest(vector<int> &num, int target) {
		sort(num.begin(), num.end());
		int sum = 0, result = 0;
		int distance = numeric_limits<int>::max();
		for (int i = 0; i < num.size(); i++){
			if (i > 0 && num[i] == num[i - 1]){
				continue;
			}
			int j = i + 1;
			int k = num.size() - 1;
			while (j < k){
				sum = num[i] + num[j] + num[k];
				if (sum == target){
					return sum;
				}
				if (sum < target){
					if ((target - sum) < distance){
						result = sum;
						distance = target - sum;
					}
					j++;
				}
				else{
					if ((sum - target) < distance){
						result = sum;
						distance = sum - target;
					}
					k--;
				}
			}
		}
		return result;
	}
};