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).

package leetcode;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ThreeSumCloset {
    /**
     * two pointers 最优解法为o(n^2)
     * 
     * @param nums
     * @param target
     * @return
     */
    public static int threeSumCloset(int[] nums, int target) {
        Arrays.sort(nums);// 数组进行排序
        int len = nums.length;
        int result = nums[0] + nums[1] + nums[len - 1];
        for (int i = 0; i < len - 2; i++) {
            int start = i + 1;
            int end = len - 1;// 尾指针
            while (start < end) {
                int sum = nums[i] + nums[start] + nums[end];
                if (sum < target) {
                    start++;
                } else if (sum > target) {
                    end--;
                } else {
                    return sum;
                }
                if (Math.abs(sum - target) < Math.abs(result - target)) {
                    result = sum;
                }
            }

        }

        return result;
    }

    public static void main(String[] args) {
        int[] nums = { -1, 2, 1, -4 };
        System.out.println(threeSumCloset(nums, 3));

    }
}