ThreeSumClosest.java

package array;

import java.util.Arrays;

/**
 * Description: https://leetcode.com/problems/3sum-closest
 * Difficulty: Medium
 * Time complexity: O(n^2)
 * Space complexity: O(1)
 */
public class ThreeSumClosest {

    public int threeSumClosest(int[] nums, int target) {
        Arrays.sort(nums);

        int minDiff = Integer.MAX_VALUE;
        int closestSum = 0;

        for (int i = 0; i < nums.length - 2; i++) {
            int left = i + 1;
            int right = nums.length - 1;

            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                int diff = Math.abs(sum - target);
                if (diff < minDiff) {
                    minDiff = diff;
                    closestSum = sum;
                }

                if (sum > target) {
                    right--;
                } else if (sum < target) {
                    left++;
                } else {
                    return sum;
                }
            }
        }

        return closestSum;
    }
}