_15_3sum.java

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

public class _15_3sum {
    public List<List<Integer>> threeSum(int[] nums) {
        Arrays.sort(nums);
        List<List<Integer>> result = new ArrayList<>();
        for(int i = 0; i<= nums.length-2; i++){
            int left = i+1;
            int right = nums.length - 1;
            if(i>0 && nums[i]==nums[i-1])continue;
            while(left<right){
                int sum = nums[i]+nums[left]+nums[right];
                if(sum==0){
                    result.add(Arrays.asList(nums[i], nums[left], nums[right]));
                    while(left<right && nums[left]==nums[left+1])left++;
                    while(left<right && nums[right]==nums[right-1])right--;
                    left++;
                    right--;
                }
                if(sum<0)left++;
                else if(sum>0) right--;
            }
        }
        return result;
    }
}