15.3-sum.java

import java.util.Arrays;

/*
 * @lc app=leetcode id=15 lang=java
 *
 * [15] 3Sum
 */

// @lc code=start
class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        if (nums.length == 0) {
            return result;
        }

        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            if (i > 0 && nums[i] == nums[i - 1]) continue;

            int left = i + 1;
            int right = nums.length - 1;

            while (left < right) {
                if (nums[i] + nums[left] + nums[right] == 0) {
                    result.add(new ArrayList<>(Arrays.asList(nums[i], nums[left], nums[right])));
                    while (left < right && nums[left + 1] == nums[left]) left++;
                    while (left < right && nums[right - 1] == nums[right]) right--;
                    left++;
                    right--;
                } else if (nums[i] + nums[left] + nums[right] < 0) {
                    left++;
                } else {
                    right--;
                }
            }
        }

        return result;
    }
}
// @lc code=end