3 Sum Closest 解答

Question

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.

Example

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).

Solution

Similar with 3 Sum. Time complexity is O(n²)

public class Solution {
    public int threeSumClosest(int[] numbers ,int target) {
        int length = numbers.length;
        Arrays.sort(numbers);
        int min = Integer.MAX_VALUE;
        int result = numbers[0] + numbers[1] + numbers[2];
        for (int i = 0; i < length - 2; i++) {
            if (i > 0 && numbers[i] == numbers[i - 1])
                continue;
            int l = i + 1, r = length - 1;
            while (l < r) {
                while (l < r && numbers[l] == numbers[l + 1])
                    l++;
                while (l < r && numbers[r] == numbers[r - 1])
                    r--;
                int sum = numbers[i] + numbers[l] + numbers[r];
                if (sum > target)
                    r--;
                else if (sum < target)
                    l++;
                else
                    return target;
                int tmp = Math.abs(sum - target);
                if (tmp < min) {
                    min = tmp;
                    result = sum;
                }
            }
        }
        return result;
    }
}