//给你一个包含 n 个整数的数组 nums，判断 nums 中是否存在三个元素 a，b，c ，使得 a + b + c = 0 ？请你找出所有满足条件且不重复
//的三元组。 
//
// 注意：答案中不可以包含重复的三元组。 
//
// 
//
// 示例： 
//
// 给定数组 nums = [-1, 0, 1, 2, -1, -4]，
//
//满足要求的三元组集合为：
//[
//  [-1, 0, 1],
//  [-1, -1, 2]
//]
// 
// Related Topics 数组 双指针

package ;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

//Java：三数之和
public class P15ThreeSum {
    public static void main(String[] args) {
        Solution solution = new P15ThreeSum().new Solution();
        // TO TEST
        int[] nums = {-1, 0, 1, 2, -1, -4};
        List<List<Integer>> res = solution.threeSum(nums);
        res.forEach(n -> {
            n.forEach(m -> {
                System.out.print(m + " ");
            });
        });
    }

    //leetcode submit region begin(Prohibit modification and deletion)
    class Solution {
        public List<List<Integer>> threeSum(int[] nums) {
            if (nums == null || nums.length == 0) {
                return new ArrayList<>();
            }
            Arrays.sort(nums);
            List<List<Integer>> res = new ArrayList<>();
            for (int i = 0; i < nums.length; i++) {
                if (i == 0 || (i > 0 && nums[i] != nums[i - 1])) {
                    int l = i + 1;
                    int r = nums.length - 1;
                    while (l < r) {
                        int temp = nums[i] + nums[l] + nums[r];
                        if (temp == 0) {
                            res.add(Arrays.asList(nums[i], nums[l], nums[r]));
                            while (l < r && nums[l] == nums[l + 1]) l++;
                            while (l < r && nums[r] == nums[r - 1]) r--;
                            l++;
                            r--;
                        } else if (temp < 0) {
                            while(l<r && nums[l] == nums[l+1]) l++;
                            l++;
                        } else {
                            while(l<r && nums[r] == nums[r-1]) r--;
                            r--;
                        }
                    }
                }
            }
            return res;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}