3Sum.java

//15. 3Sum

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