LeetCode-in-All

15. 3Sum

Medium

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

Notice that the solution set must not contain duplicate triplets.

Example 1:

Input: nums = [-1,0,1,2,-1,-4]

Output: [[-1,-1,2],[-1,0,1]]

Example 2:

Input: nums = []

Output: []

Example 3:

Input: nums = [0]

Output: []

Constraints:

• 0 <= nums.length <= 3000
• -105 <= nums[i] <= 105

Solution

public class Solution {
    public IList<IList<int>> ThreeSum(int[] nums) {
        Array.Sort(nums);
        int len = nums.Length;
        IList<IList<int>> result = new List<IList<int>>();

        for (int i = 0; i < len - 2; i++) {
            int l = i + 1;
            int r = len - 1;

            while (r > l) {
                int sum = nums[i] + nums[l] + nums[r];

                if (sum < 0) {
                    l++;
                } else if (sum > 0) {
                    r--;
                } else {
                    IList<int> list = new List<int> { nums[i], nums[l], nums[r] };
                    result.Add(list);

                    while (l < r && nums[l + 1] == nums[l]) {
                        l++;
                    }

                    while (r > l && nums[r - 1] == nums[r]) {
                        r--;
                    }

                    l++;
                    r--;
                }
            }

            while (i < len - 1 && nums[i + 1] == nums[i]) {
                i++;
            }
        }

        return result;
    }
}

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