Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
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
public class Solution {
private HashSet<string> set = new HashSet<string>();
public IList<IList<int>> ThreeSum(int[] nums) {
Array.Sort(nums);
var res = new List<IList<int>>();
for(int i=0;i<nums.Length-2;i++){
if(nums[i]>0){
break;
}
if(i > 0 && nums[i] == nums[i-1]){
continue;
}
int sum = -1 * nums[i];
for(int j=i+1, k = nums.Length-1;j<k;){
if(nums[j]+nums[k]==sum){
if(set.Contains(GetKey(nums[i], nums[j], nums[k]))){
j++;
continue;
}
res.Add(BuildList(nums[i],nums[j],nums[k]));
set.Add(GetKey(nums[i], nums[j], nums[k]));
j++;
}
else if((nums[j]+nums[k])<sum){
while(j<nums.Length-1){
if(nums[j]==nums[j+1]){
j++;
}
else{
break;
}
}
j++;
}
else{
while(k>0){
if(nums[k]==nums[k-1]){
k--;
}
else{
break;
}
}
k--;
}
}
}
return res;
}
private string GetKey(int a, int b, int c){
return a.ToString()+":"+b.ToString()+":"+c.ToString();
}
private List<int> BuildList(int a, int b, int c){
var res = new List<int>();
res.Add(a);
res.Add(b);
res.Add(c);
return res;
}
}Time Complexity: O(n^2)
Space Complexity: O(n)
