3Sum Closest 解答

Question

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

和3Sum的思路基本一样。也是固定起点后，双指针遍历。

 1 public class Solution {
 2     public int threeSumClosest(int[] nums, int target) {
 3         if (nums == null || nums.length < 3) {
 4             return 0;
 5         }
 6         int length = nums.length;
 7         Arrays.sort(nums);
 8         int min = Integer.MAX_VALUE;
 9         int result = nums[0] + nums[1] + nums[2];
10         for (int i = 0; i < length - 2; i++) {
11             // Avoid duplicates
12             if (i > 0 && nums[i] == nums[i - 1]) {
13                 continue;
14             }
15             int l = i + 1, r = length - 1;
16             while (l < r) {
17                 int sum = nums[i] + nums[l] + nums[r];
18                 int sub = Math.abs(sum - target);
19                 if (sub == 0) {
20                     return sum;
21                 } else if (min > sub) {
22                     min = sub;
23                     result = sum;
24                 }
25                 if (sum > target) {
26                     r--;
27                     // Avoid duplicates
28                     while (l < r && nums[r] == nums[r + 1]) {
29                         r--;
30                     }
31                 } else if (sum < target) {
32                     l++;
33                     // Avoid duplicates
34                     while (l < r && nums[l] == nums[l - 1]) {
35                         l++;
36                     }
37                 }
38             }
39         }
40         return result;
41     }
42 }