Last updated on October 5th, 2024 at 09:10 pm

Here, We see 4Sum LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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4Sum LeetCode Solution

Problem Statement

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

• 0 <= a, b, c, d < n
• a, b, c, and d are distinct.
• nums[a] + nums[b] + nums[c] + nums[d] == target

You may return the answer in any order.

Example 1:
Input: nums = [1,0,-1,0,-2,2], target = 0
Output: [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]

Example 2:
Input: nums = [2,2,2,2,2], target = 8
Output: [[2,2,2,2]]

1. 4Sum Leetcode Solution C++

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> total;
        int n = nums.size();
        if(n<4)  return total;
        sort(nums.begin(),nums.end());
        for(int i=0;i<n-3;i++)
        {
            if(i>0&&nums[i]==nums[i-1]) continue;
            if(nums[i]+nums[i+1]+nums[i+2]+nums[i+3]>target) break;
            if(nums[i]+nums[n-3]+nums[n-2]+nums[n-1]<target) continue;
            for(int j=i+1;j<n-2;j++)
            {
                if(j>i+1&&nums[j]==nums[j-1]) continue;
                if(nums[i]+nums[j]+nums[j+1]+nums[j+2]>target) break;
                if(nums[i]+nums[j]+nums[n-2]+nums[n-1]<target) continue;
                int left=j+1,right=n-1;
                while(left<right){
                    int sum=nums[left]+nums[right]+nums[i]+nums[j];
                    if(sum<target) left++;
                    else if(sum>target) right--;
                    else{
                        total.push_back(vector<int>{nums[i],nums[j],nums[left],nums[right]});
                        do{left++;}while(nums[left]==nums[left-1]&&left<right);
                        do{right--;}while(nums[right]==nums[right+1]&&left<right);
                    }
                }
            }
        }
        return total;
    }
};

2. 4Sum Leetcode Solution Java

class Solution {
public List<List<Integer>> fourSum(int[] nums, int target) {
		ArrayList<List<Integer>> res = new ArrayList<List<Integer>>();
		int len = nums.length;
		if (nums == null || len < 4)
			return res;
		Arrays.sort(nums);
		int max = nums[len - 1];
		if (4 * nums[0] > target || 4 * max < target)
			return res;
		int i, z;
		for (i = 0; i < len; i++) {
			z = nums[i];
			if (i > 0 && z == nums[i - 1])
				continue;
			if (z + 3 * max < target)
				continue;
			if (4 * z > target)
				break;
			if (4 * z == target) {
				if (i + 3 < len && nums[i + 3] == z)
					res.add(Arrays.asList(z, z, z, z));
				break;
			}
			threeSumForFourSum(nums, target - z, i + 1, len - 1, res, z);
		}
		return res;
	}
	public void threeSumForFourSum(int[] nums, int target, int low, int high, ArrayList<List<Integer>> fourSumList,
			int z1) {
		if (low + 1 >= high)
			return;
		int max = nums[high];
		if (3 * nums[low] > target || 3 * max < target)
			return;
		int i, z;
		for (i = low; i < high - 1; i++) {
			z = nums[i];
			if (i > low && z == nums[i - 1])
				continue;
			if (z + 2 * max < target)
				continue;
			if (3 * z > target)
				break;
			if (3 * z == target) {
				if (i + 1 < high && nums[i + 2] == z)
					fourSumList.add(Arrays.asList(z1, z, z, z));
				break;
			}
			twoSumForFourSum(nums, target - z, i + 1, high, fourSumList, z1, z);
		}
	}
	public void twoSumForFourSum(int[] nums, int target, int low, int high, ArrayList<List<Integer>> fourSumList,
			int z1, int z2) {
		if (low >= high)
			return;
		if (2 * nums[low] > target || 2 * nums[high] < target)
			return;
		int i = low, j = high, sum, x;
		while (i < j) {
			sum = nums[i] + nums[j];
			if (sum == target) {
				fourSumList.add(Arrays.asList(z1, z2, nums[i], nums[j]));
				x = nums[i];
				while (++i < j && x == nums[i])
					;
				x = nums[j];
				while (i < --j && x == nums[j])
					;
			}
			if (sum < target)
				i++;
			if (sum > target)
				j--;
		}
		return;
	}
}

3. 4Sum Leetcode Solution JavaScript

var fourSum = function(nums, target) {
    nums.sort((a, b) => a - b);
    const result = []
    for(let i = 0; i < nums.length - 3; i++) {
        for(let j = i + 1; j < nums.length - 2; j++) {
            let low = j + 1;
            let high = nums.length - 1

            while(low < high) {
                const sum = nums[i] + nums[j] + nums[low] + nums[high];
                if(sum === target) {
                    result.push([nums[i], nums[j], nums[low], nums[high]])
                    while(nums[low] === nums[low + 1]) low++;
                    while(nums[high] === nums[high - 1]) high--;
                    low++;
                    high--;
                } else if(sum < target) {
                    low++
                } else {
                    high--
                }
            }   
            while(nums[j] === nums[j + 1]) j++;
        }   
        while(nums[i] === nums[i + 1]) i++;
    }
    return result
};

4. 4Sum Leetcode Solution Python

class Solution(object):
    def fourSum(self, nums, target):
        nums.sort()
        results = []
        self.findNsum(nums, target, 4, [], results)
        return results
    def findNsum(self, nums, target, N, result, results):
        if len(nums) < N or N < 2: return
        if N == 2:
            l,r = 0,len(nums)-1
            while l < r:
                if nums[l] + nums[r] == target:
                    results.append(result + [nums[l], nums[r]])
                    l += 1
                    r -= 1
                    while l < r and nums[l] == nums[l - 1]:
                        l += 1
                    while r > l and nums[r] == nums[r + 1]:
                        r -= 1
                elif nums[l] + nums[r] < target:
                    l += 1
                else:
                    r -= 1
        else:
            for i in range(0, len(nums)-N+1):
                if target < nums[i]*N or target > nums[-1]*N:
                    break
                if i == 0 or i > 0 and nums[i-1] != nums[i]:
                    self.findNsum(nums[i+1:], target-nums[i], N-1, result+[nums[i]], results)
        return