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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;
}
}