59 · 最接近的三数之和（相向双指针）

链接：https://www.lintcode.com/problem/59/description

题解：

class Solution {
public:
    /**
     * @param numbers: Give an array numbers of n integer
     * @param target: An integer
     * @return: return the sum of the three integers, the sum closest target.
     */
    int threeSumClosest(vector<int> &numbers, int target) {
        // write your code here
        int len = numbers.size();
        if (len <= 0) {
            return 0;
        }
        sort(numbers.begin(), numbers.end());
        int result = INT_MAX;
        for (int i = 0; i < numbers.size(); ++i) {
            int l = i + 1;
            int r = len-1;
            int sum = numbers[i];
            while (l < r) {
                sum = numbers[i] + numbers[l] + numbers[r];
		if (abs(sum-target) < abs(result-target)) {
		    result = sum;
		}
                if (sum > target) {
		    --r;
                } else if (sum < target) {
                    ++l;
                } else {
                    return target;
                }
            }
        }
        return result;
    }
};