Leetcode and Lintcode

3Sum Closest

Problem:

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).

Leetcode link
Lintcode link

Solution:

Sort the list first, which takes O(Nlog N). Then go through the sorted list， for each integer “nums[i]” in the list,
narrow the range from the integers at index i and the end of the list. It takes O(n^2)

Use a ‘min’ variable to record the minimum difference, and a ‘result’ variable to record the sum with the minimum difference.

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/*************************************************************************
	> File Name: ThreeSumClosest.java
	> Author: Yao Zhang 
	> Mail: psyyz10@163.com 
	> Created Time: Wed 11 Nov 23:20:11 2015
 ************************************************************************/

public class ThreeSumClosest{
    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 start = i + 1;
            int end = nums.length - 1;
                      
            while (start < end){
                int sum = nums[i] + nums[start] + nums[end];
                int diff = Math.abs(sum - target); 
                      
                if (diff < min){
                    min = diff;
                    result = sum;
                }
                      
                if (sum == target)
                    return sum;
                else if (sum < target)
                    start++;
                else 
                    end--;
            }         
        }             
                      
        return result;  
    }
}