[LintCode/LeetCode] 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.

Notice

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

Example

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).

Challenge

O(n^2) time, O(1) extra space

Note

这个题和3Sum的做法基本一样，只要在循环内计算和target最接近的和sum，并赋值更新返回值min即可。

Solution

public class Solution {
    public int threeSumClosest(int[] A ,int target) {
        int min = Integer.MAX_VALUE - target;
        if (A.length < 3) return -1;
        Arrays.sort(A);
        for (int i = 0; i <= A.length-3; i++) {
            int left = i+1, right = A.length-1;
            while (left < right) {
                int sum = A[i]+A[left]+A[right];
                if (sum == target) return sum;
                else if (sum < target) left++;
                else right--;
                min = Math.abs(min-target) < Math.abs(sum-target) ? min : sum;
            }
        }
        return min;
    }
}