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;
    }
}