3Sum Closest

Description

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).

Tags: Array, Two Pointers

思路

题意是让你从数组中找出最接近 target 的三个数的和，该题和 3Sum 的思路基本一样，先对数组进行排序，然后遍历这个排序数组，用两个指针分别指向当前元素的下一个和数组尾部，判断三者的和与 target 的差值来移动两个指针，并更新其结果，当然，如果三者的和直接与 target 值相同，那么返回 target 结果即可。

public class Solution {
    public int threeSumClosest(int[] nums, int target) {
        int delta = 0x7fffffff, res = 0;
        Arrays.sort(nums);
        int len = nums.length - 2;
        for (int i = 0; i < len; i++) {
            int left = i + 1, right = nums.length - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                int curDelta = Math.abs(sum - target);
                if (curDelta == 0) return sum;
                if (curDelta < delta) {
                    delta = curDelta;
                    res = sum;
                }
                if (sum > target) --right;
                else ++left;
            }
        }
        return res;
    }
}

结语

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