3Sum - Closest

Problem

Given an integer array nums of length n and an integer target, find three integers in nums such that the sum is closest to target.

Return the sum of the three integers.

You may assume that each input would have exactly one solution.

Examples

Example 1:

Input: nums = [-1,2,1,-4], target = 1
Output: 2
Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Example 2:

Input: nums = [0,0,0], target = 1
Output: 0
Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0).

Solution

This problem is similar to [2 Sum](two-sum).

Method 1 - Sorting with 2 Pointer Approach

This kind of problem can be solved by using a similar approach, i.e., two pointers from both left and right.

Code

Java

public int threeSumClosest(int[] nums, int target) {
    int min = Integer.MAX_VALUE;
    int result = 0;

    Arrays.sort(nums);

    for (int i = 0; i < nums.length; i++) {
        int j = i + 1;
        int k = nums.length - 1;
        while (j < k) {
            int sum = nums[i] + nums[j] + nums[k];
            int diff = Math.abs(sum - target);

            if (diff == 0) return sum;

            if (diff < min) {
                min = diff;
                result = sum;
            }
            if (sum <= target) {
                j++;
            } else {
                k--;
            }
        }
    }

    return result;
}

Complexity

• ⏰ Time complexity: O(n^2)
• 🧺 Space complexity: O(1)