Two Pointer

Question 1

Two Sum UnSorted / Sorted

Answer 1

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map map = new HashMap<>();
        int[] res = new int[2];
        for (int i = 0;i target) right--;
            if (sum < target) left++;
        }
        return res;
    }
}

Question 2

3 Sum adding up to 0

Answer 2

class Solution {
    public List> threeSum(int[] nums) {
        List> result = new ArrayList<>();
        if (nums == null || nums.length < 3){
            return result;
        }

    Arrays.sort(nums);

    for (int i = 0;i= 0 && nums[i] == nums[i-1])
            continue;

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

        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 + 1 < right && nums[left] == nums[left+1])
                left++;
                while (left < right-1 && nums[right] == nums[right-1])
                    right--;
                left++;
                right--;    
            }
            else if (sum < 0) left++;
            else  right--;
        }
    }
    return result;
} }