15. 3Sum

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

C++

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        vector<vector<int>> result;

        for (int i = 0; i < nums.size(); i++) {
            if (i >= 1 && nums[i] == nums[i-1]) {
                continue;
            }
            int left = i + 1;
            int right = nums.size() - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum == 0) {
                    result.push_back({nums[i], nums[left], nums[right]});
                }
                if (sum <= 0) {
                    left++;
                    while (left < right && nums[left] == nums[left - 1]) {
                        left++;
                    }
                }
                if (sum >= 0) {
                    right--;
                    while (left < right && nums[right] == nums[right + 1]) {
                        right--;
                    }
                }
            }
        }
        return result;
    }
};

Go

func threeSum(nums []int) [][]int {
  var result [][]int

  sort.Ints(nums)
  for i := 0; i < len(nums); i++ {
    if i >= 1 && nums[i] == nums[i-1] {
      continue
    }
    left := i + 1
    right := len(nums) - 1
    for left < right {
      sum := nums[i] + nums[left] + nums[right]
      if sum == 0 {
        result = append(result, []int{nums[i], nums[left], nums[right]})
      }
      if sum <= 0 {
        left++
        for left < right && nums[left] == nums[left-1] {
          left++
        }
      }
      if sum >= 0 {
        right--
        for left < right && nums[right] == nums[right+1] {
          right--
        }
      }
    }
  }
  return result
}

JavaScript

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var threeSum = function(nums) {
  nums.sort((a, b) => a - b)
  var result = []

  for (let i = 0; i < nums.length; i++) {
    if (i >= 1 && nums[i] === nums[i - 1]) {
      continue
    }
    let left = i + 1
    let right = nums.length - 1
    while (left < right) {
      let sum = nums[left] + nums[right] + nums[i]
      if (sum === 0) {
        result.push([nums[i], nums[left], nums[right]])
      }
      if (sum <= 0) {
        left++
        while (left < right && nums[left] === nums[left - 1]) {
          left++
        }
      }
      if (sum >= 0) {
        right--
        while (left < right && nums[right] === nums[right + 1]) {
          right--
        }
      }
    }
  }

  return result
}

Python

class Solution(object):

    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        nums.sort()
        result = []
        for i in range(len(nums) - 2):
            if i >= 1 and nums[i] == nums[i - 1]:
                continue
            left, right = i + 1, len(nums) - 1
            while left < right:
                s = nums[i] + nums[left] + nums[right]
                if s == 0:
                    result.append([nums[i], nums[left], nums[right]])
                if s <= 0:
                    left += 1
                    while left < right and nums[left] == nums[left - 1]:
                        left += 1
                if s >= 0:
                    right -= 1
                    while left < right and nums[right] == nums[right + 1]:
                        right -= 1
        return result