16. 3Sum Closest

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#leetcode #3Sum Closest

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本文介绍了一个算法问题：给定一个整数数组和一个目标值，找到数组中三个整数相加最接近目标值的和。通过排序数组并使用双指针技术，实现了高效的解决方案。

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

    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:

Tips:

sort array first, then fix a number from two sides to the middle to calculate the gap between three sum and target number.

Java Code:

public class Solution {
    public int threeSumClosest(int[] nums, int target) {
        // assume input is validate, omit code here
        //if (nums == null || nums.length < 3) {
        //    return 0;
        //}
        
        Arrays.sort(nums);
        int minVal = nums[0] + nums[1] + nums[2];
        int minGap = Math.abs(minVal - target);
        
        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];
                
                if (sum == target) {
                    return target;
                }
                if (sum > target) {
                    right--;
                } else {
                    left++;
                }
                if (Math.abs(sum - target) < minGap) {
                    minVal = sum;
                    minGap = Math.abs(sum - target);
                }
            }
        }
        
        return minVal;
    }
}