16. 3Sum Closest

Given an array nums of n integers 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.

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution

(1) Java

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        Arrays.sort(nums);
        long rst = Integer.MAX_VALUE;
        for (int i = 0; i < nums.length-2; i++) {
            if (i != 0 && nums[i] == nums[i-1]) {
                continue;
            }
            int num1 = nums[i];
            int left = i+1;
            int right = nums.length-1;
            while (left < right) {
                int sum = num1+nums[left]+nums[right];
                if (sum == target) {
                    return sum;
                }
                rst = Math.abs(target-sum) < Math.abs(target-rst) ? sum : rst;
                if (sum < target) {
                    while (left < right && nums[left] == nums[left+1]) {
                        left++;
                    }
                    left++;
                } else {
                    while (left < right && nums[right] == nums[right-1]) {
                        right--;
                    }
                    right--;
                }
            }
        }
        return (int)rst;
    }
}

(2) Python

class Solution(object):
    def threeSumClosest(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        nums.sort()
        rst = nums[0]+nums[1]+nums[2]
        for i in range(len(nums)-2):
            left = i+1
            right = len(nums)-1
            while left < right:
                sum = nums[i]+nums[left]+nums[right]
                if sum == target:
                    return sum
                if abs(target-sum) < abs(target-rst):
                    rst = sum
                if sum < target:
                    left += 1
                else:
                    right -= 1
        return rst

(3) Scala

object Solution {
    def threeSumClosest(nums: Array[Int], target: Int): Int = {
        nums.length match {
            case 3 => return nums.sum
            case _ => {
                scala.util.Sorting.quickSort(nums)
                var rst = nums(0)+nums(1)+nums(2)
                for (i <- 0 until nums.length-2) {
                    if (i == 0 || nums(i) != nums(i-1)) {
                        var left = i+1
                        var right = nums.length-1
                        while (left < right) {
                            var sum = nums(i)+nums(left)+nums(right)
                            if (sum == target) {
                                return sum
                            } else {
                                rst = if (math.abs(target-sum) < math.abs(target-rst)) sum else rst
                                if (sum < target) {
                                    while (left < right && nums(left) == nums(left+1)) {
                                        left += 1
                                    }
                                    left += 1
                                } else {
                                    while (left < right && nums(right) == nums(right-1)) {
                                        right -= 1
                                    } 
                                    right -= 1
                                }
                            }
                        }
                    }
                }
                rst
            }
        }
    }
}