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).

解题思路就是枚举出所有组合，然后不断更新优化bestSum

public class Solution {
    /**
     * @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.
     */
    public int threeSumClosest(int[] numbers, int target) {
        // write your code here
         if (numbers == null || numbers.length < 3) {
            return -1;
        }
        
        
        Arrays.sort(numbers);
        int bestSum = numbers[0] + numbers[1] + numbers[2];
        for (int i = 0; i < numbers.length; i++) {
            int start = i + 1, end = numbers.length - 1;
            while (start < end) {
                int sum = numbers[i] + numbers[start] + numbers[end];
                if (Math.abs(target - sum) < Math.abs(target - bestSum)) {
                    bestSum = sum;
                }
                if (sum < target) {
                    start++;
                } else {
                    end--;
                }
            }
        }

        return bestSum;
    }
}