16. 3Sum Closest

Problem Description

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.

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).

Python Solution

def threeSumClosest(nums: List[int], target: int) -> int:
    nums.sort()
    n = len(nums)
    closest_sum = float('inf')
    
    for i in range(n - 2):
        left, right = i + 1, n - 1
        
        while left < right:
            current_sum = nums[i] + nums[left] + nums[right]
            
            if current_sum == target:
                return current_sum
            
            if abs(current_sum - target) < abs(closest_sum - target):
                closest_sum = current_sum
            
            if current_sum < target:
                left += 1
            else:
                right -= 1
    
    return closest_sum
    

Java Solution

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        Arrays.sort(nums);
        int n = nums.length;
        int closestSum = Integer.MAX_VALUE;
        
        for (int i = 0; i < n - 2; i++) {
            int left = i + 1;
            int right = n - 1;
            
            while (left < right) {
                int currentSum = nums[i] + nums[left] + nums[right];
                
                if (currentSum == target) {
                    return currentSum;
                }
                
                if (closestSum == Integer.MAX_VALUE ||
                    Math.abs(currentSum - target) < Math.abs(closestSum - target)) {
                    closestSum = currentSum;
                }
                
                if (currentSum < target) {
                    left++;
                } else {
                    right--;
                }
            }
        }
        
        return closestSum;
    }
}
    

C++ Solution

class Solution {
public:
    int threeSumClosest(vector& nums, int target) {
        sort(nums.begin(), nums.end());
        int n = nums.size();
        int closestSum = INT_MAX;
        
        for (int i = 0; i < n - 2; i++) {
            int left = i + 1;
            int right = n - 1;
            
            while (left < right) {
                int currentSum = nums[i] + nums[left] + nums[right];
                
                if (currentSum == target) {
                    return currentSum;
                }
                
                if (closestSum == INT_MAX ||
                    abs(currentSum - target) < abs(closestSum - target)) {
                    closestSum = currentSum;
                }
                
                if (currentSum < target) {
                    left++;
                } else {
                    right--;
                }
            }
        }
        
        return closestSum;
    }
};
    

JavaScript Solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var threeSumClosest = function(nums, target) {
    nums.sort((a, b) => a - b);
    const n = nums.length;
    let closestSum = Infinity;
    
    for (let i = 0; i < n - 2; i++) {
        let left = i + 1;
        let right = n - 1;
        
        while (left < right) {
            const currentSum = nums[i] + nums[left] + nums[right];
            
            if (currentSum === target) {
                return currentSum;
            }
            
            if (Math.abs(currentSum - target) < Math.abs(closestSum - target)) {
                closestSum = currentSum;
            }
            
            if (currentSum < target) {
                left++;
            } else {
                right--;
            }
        }
    }
    
    return closestSum;
};
    

C# Solution

public class Solution {
    public int ThreeSumClosest(int[] nums, int target) {
        Array.Sort(nums);
        int n = nums.Length;
        int closestSum = int.MaxValue;
        
        for (int i = 0; i < n - 2; i++) {
            int left = i + 1;
            int right = n - 1;
            
            while (left < right) {
                int currentSum = nums[i] + nums[left] + nums[right];
                
                if (currentSum == target) {
                    return currentSum;
                }
                
                if (closestSum == int.MaxValue ||
                    Math.Abs(currentSum - target) < Math.Abs(closestSum - target)) {
                    closestSum = currentSum;
                }
                
                if (currentSum < target) {
                    left++;
                } else {
                    right--;
                }
            }
        }
        
        return closestSum;
    }
}