3Sum

15. 3Sum

LintCode-57.3Sum

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note: The solution set must not contain duplicate triplets.

For example, given array S = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

class Solution {
    func threeSum(_ nums: [Int]) -> [[Int]] {
        let nums = nums.sorted { $0 < $1 }
        var result: [[Int]] = []
        
        if nums.count < 3 {
            return []
        }
        
        for i in 0..<nums.count - 2 {
            if i > 0 && nums[i] == nums[i - 1] {
                continue
            }
            
            var low = i + 1, high = nums.count - 1
            while low < high {
                let sum = nums[i] + nums[low] + nums[high]
                
                if sum == 0 {
                    result.append([nums[i], nums[low], nums[high]])
                    
                    low += 1
                    high -= 1
                    
                    while low < high && nums[low] == nums[low - 1] {
                        low += 1
                    }
                    while low < high && nums[high] == nums[high + 1] {
                        high -= 1
                    }
                } else if sum < 0 {
                    low += 1
                } else {
                    high -= 1
                }
            }
        }
        
        return result
    }
}

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

        for (int i = 0; i < nums.length - 2; i++) {
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            
            int low = i + 1, high = nums.length - 1;
            while (low < high) {
                int sum = nums[i] + nums[low] + nums[high];

                if (sum == 0) {
                    List<Integer> list = new ArrayList<>();
                    list.add(nums[i]);
                    list.add(nums[low]);
                    list.add(nums[high]);
                    
                    result.add(list);
                    
                    low++;
                    high--;
                    
                    while (low < high && nums[low] == nums[low - 1]) {
                        low++;
                    }
                    
                    while (low < high && nums[high] == nums[high + 1]) {
                        high--;
                    }
                } else if (sum < 0) {
                    low++;
                } else {
                    high--;
                }
             }
        }
        
        return result;
    }
}

Hope this helps,
Michael