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Sri Hari: Batch-7/Added articles (#4148)
* Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles * Batch-7/Neetcode-ALL/Added-articles
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‎articles/4sum.md

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@@ -96,6 +96,35 @@ class Solution {
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}
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```
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```csharp
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public class Solution {
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public List<List<int>> FourSum(int[] nums, int target) {
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int n = nums.Length;
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Array.Sort(nums);
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HashSet<(int, int, int, int)> res = new HashSet<(int, int, int, int)>();
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for (int a = 0; a < n; a++) {
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for (int b = a + 1; b < n; b++) {
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for (int c = b + 1; c < n; c++) {
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for (int d = c + 1; d < n; d++) {
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long sum = (long)nums[a] + nums[b] + nums[c] + nums[d];
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if (sum == target) {
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res.Add((nums[a], nums[b], nums[c], nums[d]));
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}
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}
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}
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}
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}
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var result = new List<List<int>>();
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foreach (var quad in res) {
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result.Add(new List<int> { quad.Item1, quad.Item2, quad.Item3, quad.Item4 });
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}
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return result;
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}
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}
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```
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::tabs-end
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### Time & Space Complexity
@@ -287,6 +316,58 @@ class Solution {
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}
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```
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```csharp
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public class Solution {
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public List<List<int>> FourSum(int[] nums, int target) {
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Array.Sort(nums);
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Dictionary<int, int> count = new Dictionary<int, int>();
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foreach (int num in nums) {
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if (!count.ContainsKey(num)) {
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count[num] = 0;
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}
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count[num]++;
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}
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List<List<int>> res = new List<List<int>>();
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for (int i = 0; i < nums.Length; i++) {
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count[nums[i]]--;
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if (i > 0 && nums[i] == nums[i - 1]) continue;
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for (int j = i + 1; j < nums.Length; j++) {
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count[nums[j]]--;
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if (j > i + 1 && nums[j] == nums[j - 1]) continue;
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for (int k = j + 1; k < nums.Length; k++) {
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count[nums[k]]--;
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if (k > j + 1 && nums[k] == nums[k - 1]) continue;
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long fourth = (long)target - (long)nums[i] - (long)nums[j] - (long)nums[k];
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if (fourth > int.MaxValue || fourth < int.MinValue) {
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continue;
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}
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if (count.ContainsKey((int)fourth) && count[(int)fourth] > 0) {
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res.Add(new List<int> { nums[i], nums[j], nums[k], (int)fourth });
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}
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}
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for (int k = j + 1; k < nums.Length; k++) {
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count[nums[k]]++;
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}
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}
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for (int j = i + 1; j < nums.Length; j++) {
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count[nums[j]]++;
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}
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}
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return res;
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}
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}
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```
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::tabs-end
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### Time & Space Complexity
@@ -448,6 +529,42 @@ class Solution {
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}
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```
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```csharp
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public class Solution {
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public List<List<int>> FourSum(int[] nums, int target) {
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Array.Sort(nums);
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List<List<int>> res = new List<List<int>>();
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int n = nums.Length;
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for (int i = 0; i < n; i++) {
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if (i > 0 && nums[i] == nums[i - 1]) continue;
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for (int j = i + 1; j < n; j++) {
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if (j > i + 1 && nums[j] == nums[j - 1]) continue;
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int left = j + 1, right = n - 1;
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while (left < right) {
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long sum = (long)nums[i] + nums[j] + nums[left] + nums[right];
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if (sum == target) {
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res.Add(new List<int> { nums[i], nums[j], nums[left], nums[right] });
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left++;
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right--;
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while (left < right && nums[left] == nums[left - 1]) left++;
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while (left < right && nums[right] == nums[right + 1]) right--;
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} else if (sum < target) {
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left++;
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} else {
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right--;
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}
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}
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}
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}
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return res;
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}
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}
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```
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::tabs-end
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### Time & Space Complexity
@@ -637,6 +754,52 @@ class Solution {
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}
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```
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```csharp
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public class Solution {
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private List<List<int>> res;
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private List<int> quad;
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public List<List<int>> FourSum(int[] nums, int target) {
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Array.Sort(nums);
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res = new List<List<int>>();
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quad = new List<int>();
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KSum(nums, 4, 0, target);
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return res;
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}
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private void KSum(int[] nums, int k, int start, long target) {
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if (k == 2) {
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int l = start, r = nums.Length - 1;
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while (l < r) {
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long sum = (long)nums[l] + nums[r];
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if (sum < target) {
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l++;
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} else if (sum > target) {
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r--;
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} else {
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List<int> newQuad = new List<int>(quad);
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newQuad.Add(nums[l]);
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newQuad.Add(nums[r]);
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res.Add(newQuad);
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l++;
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r--;
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while (l < r && nums[l] == nums[l - 1]) l++;
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while (l < r && nums[r] == nums[r + 1]) r--;
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}
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}
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return;
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}
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for (int i = start; i < nums.Length - k + 1; i++) {
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if (i > start && nums[i] == nums[i - 1]) continue;
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quad.Add(nums[i]);
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KSum(nums, k - 1, i + 1, target - nums[i]);
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quad.RemoveAt(quad.Count - 1);
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}
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}
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}
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```
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::tabs-end
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### Time & Space Complexity

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