3Sum Closest

描述

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).

分析

先排序，然后左右夹逼，复杂度 O(n2)O(n^2)。

代码

  1. // 3Sum Closest
  2. // 先排序，然后左右夹逼
  3. // Time Complexity: O(n^2), Space Complexity: O(1)
  4. public class Solution {
  5.     public int threeSumClosest(int[] nums, int target) {
  6.         int result = 0;
  7.         int minGap = Integer.MAX_VALUE;
  8.         Arrays.sort(nums);
  10.         for (int i = 0; i < nums.length - 1; ++i) {
  11.             int j = i + 1;
  12.             int k = nums.length - 1;
  14.             while(j < k) {
  15.                 final int sum = nums[i] + nums[j] + nums[k];
  16.                 final int gap = Math.abs(sum - target);
  17.                 if (gap < minGap) {
  18.                     result = sum;
  19.                     minGap = gap;
  20.                 }
  22.                 if (sum < target) ++j;
  23.                 else              --k;
  24.             }
  25.         }
  26.         return result;
  27.     }
  28. }

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/linear-list/array/3sum-closest.html