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。

 public class Solution {
     public int threeSumClosest(int[] nums, int target) {
         if (nums == null || nums.length < 3) {
             return 0;
         }
         int length = nums.length;
         Arrays.sort(nums);
         int min = Integer.MAX_VALUE;
         int result = nums[0] + nums[1] + nums[2];
         for (int i = 0; i < length - 2; i++) {
             // Avoid duplicates
             if (i > 0 && nums[i] == nums[i - 1]) {
                 continue;
             }
             int l = i + 1, r = length - 1;
             while (l < r) {
                 int sum = nums[i] + nums[l] + nums[r];
                 int sub = Math.abs(sum - target);
                 if (sub == 0) {
                     return sum;
                 } else if (min > sub) {
                     min = sub;
                     result = sum;
                 }
                 if (sum > target) {
                     r--;
                     // Avoid duplicates
                     while (l < r && nums[r] == nums[r + 1]) {
                         r--;
                     }
                 } else if (sum < target) {
                     l++;
                     // Avoid duplicates
                     while (l < r && nums[l] == nums[l - 1]) {
                         l++;
                     }
                 }
             }
         }
         return result;
     }
 }