15. 3Sum | LeetCode | Top Interview 150 | Coding Questions

Problem Link

https://leetcode.com/problems/3sum/

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Detailed Step-by-Step Explanation

https://leetcode.com/problems/3sum/solutions/7456672/most-optimal-solution-ever-pointers-beat-lyku

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Solution

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {

        List<List<Integer>> ans = new ArrayList<>();
        int n = nums.length;
        Arrays.sort(nums);

        for (int i = 0; i < n; i++) {

            // Skip duplicate first elements
            if (i != 0 && nums[i] == nums[i - 1]) continue;

            int j = i + 1;
            int k = n - 1;

            while (j < k) {
                int sum = nums[i] + nums[j] + nums[k];

                if (sum < 0) {
                    j++;
                } else if (sum > 0) {
                    k--;
                } else {
                    ans.add(Arrays.asList(nums[i], nums[j], nums[k]));
                    j++;
                    k--;

                    // Skip duplicate second elements
                    while (j < k && nums[j] == nums[j - 1]) j++;

                    // Skip duplicate third elements
                    while (j < k && nums[k] == nums[k + 1]) k--;
                }
            }
        }

        return ans;
    }
}