Added tasks 1-46

LeetCodeNet/G0001_0100/S0001_two_sum/readme.md

@@ -0,0 +1,59 @@
+[![](https://img.shields.io/github/stars/LeetCode-in-Net/LeetCode-in-Net?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net)
+[![](https://img.shields.io/github/forks/LeetCode-in-Net/LeetCode-in-Net?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net/fork)
+
+## 1\. Two Sum
+
+Easy
+
+Given an array of integers `nums` and an integer `target`, return _indices of the two numbers such that they add up to `target`_.
+
+You may assume that each input would have **_exactly_ one solution**, and you may not use the _same_ element twice.
+
+You can return the answer in any order.
+
+**Example 1:**
+
+**Input:** nums = [2,7,11,15], target = 9
+
+**Output:** [0,1]
+
+**Explanation:** Because nums[0] + nums[1] == 9, we return [0, 1]. 
+
+**Example 2:**
+
+**Input:** nums = [3,2,4], target = 6
+
+**Output:** [1,2] 
+
+**Example 3:**
+
+**Input:** nums = [3,3], target = 6
+
+**Output:** [0,1] 
+
+**Constraints:**
+
+*   <code>2 <= nums.length <= 10<sup>4</sup></code>
+*   <code>-10<sup>9</sup> <= nums[i] <= 10<sup>9</sup></code>
+*   <code>-10<sup>9</sup> <= target <= 10<sup>9</sup></code>
+*   **Only one valid answer exists.**
+
+**Follow-up:** Can you come up with an algorithm that is less than <code>O(n<sup>2</sup>)</code> time complexity?
+
+## Solution
+
+```csharp
+public class Solution {
+    public int[] TwoSum(int[] numbers, int target) {
+        Dictionary<int, int> indexMap = new Dictionary<int, int>();
+        for (int i = 0; i < numbers.Length; i++) {
+            int requiredNum = target - numbers[i];
+            if (indexMap.ContainsKey(requiredNum)) {
+                return new int[] {indexMap[requiredNum], i};
+            }
+            indexMap[numbers[i]] = i;
+        }
+        return new int[] {-1, -1};
+    }
+}
+```

LeetCodeNet/G0001_0100/S0002_add_two_numbers/readme.md

@@ -0,0 +1,66 @@
+[![](https://img.shields.io/github/stars/LeetCode-in-Net/LeetCode-in-Net?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net)
+[![](https://img.shields.io/github/forks/LeetCode-in-Net/LeetCode-in-Net?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net/fork)
+
+## 2\. Add Two Numbers
+
+Medium
+
+You are given two **non-empty** linked lists representing two non-negative integers. The digits are stored in **reverse order**, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.
+
+You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/10/02/addtwonumber1.jpg)
+
+**Input:** l1 = [2,4,3], l2 = [5,6,4]
+
+**Output:** [7,0,8]
+
+**Explanation:** 342 + 465 = 807. 
+
+**Example 2:**
+
+**Input:** l1 = [0], l2 = [0]
+
+**Output:** [0] 
+
+**Example 3:**
+
+**Input:** l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
+
+**Output:** [8,9,9,9,0,0,0,1] 
+
+**Constraints:**
+
+*   The number of nodes in each linked list is in the range `[1, 100]`.
+*   `0 <= Node.val <= 9`
+*   It is guaranteed that the list represents a number that does not have leading zeros.
+
+## Solution
+
+```csharp
+using LeetCodeNet.Com_github_leetcode;
+
+public class Solution {
+    public ListNode AddTwoNumbers(ListNode l1, ListNode l2) {
+        ListNode dummyHead = new ListNode(0);
+        ListNode curr = dummyHead;
+        int carry = 0;
+        while (l1 != null || l2 != null) {
+            int x = (l1 != null) ? l1.val : 0;
+            int y = (l2 != null) ? l2.val : 0;
+            int sum = carry + x + y;
+            carry = sum / 10;
+            curr.next = new ListNode(sum % 10);
+            curr = curr.next;
+            if (l1 != null) l1 = l1.next;
+            if (l2 != null) l2 = l2.next;
+        }
+        if (carry > 0) {
+            curr.next = new ListNode(carry);
+        }
+        return dummyHead.next;
+    }
+}
+```

LeetCodeNet/G0001_0100/S0003_longest_substring_without_repeating_characters/readme.md

@@ -0,0 +1,75 @@
+[![](https://img.shields.io/github/stars/LeetCode-in-Net/LeetCode-in-Net?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net)
+[![](https://img.shields.io/github/forks/LeetCode-in-Net/LeetCode-in-Net?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net/fork)
+
+## 3\. Longest Substring Without Repeating Characters
+
+Medium
+
+Given a string `s`, find the length of the **longest substring** without repeating characters.
+
+**Example 1:**
+
+**Input:** s = "abcabcbb"
+
+**Output:** 3
+
+**Explanation:** The answer is "abc", with the length of 3. 
+
+**Example 2:**
+
+**Input:** s = "bbbbb"
+
+**Output:** 1
+
+**Explanation:** The answer is "b", with the length of 1. 
+
+**Example 3:**
+
+**Input:** s = "pwwkew"
+
+**Output:** 3
+
+**Explanation:** The answer is "wke", with the length of 3. Notice that the answer must be a substring, "pwke" is a subsequence and not a substring. 
+
+**Example 4:**
+
+**Input:** s = ""
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>0 <= s.length <= 5 * 10<sup>4</sup></code>
+*   `s` consists of English letters, digits, symbols and spaces.
+
+## Solution
+
+```csharp
+public class Solution {
+    public int LengthOfLongestSubstring(string s) {
+        int[] lastIndices = new int[256];
+        for (int i = 0; i < 256; i++) {
+            lastIndices[i] = -1;
+        }
+        int maxLen = 0;
+        int curLen = 0;
+        int start = 0;
+        for (int i = 0; i < s.Length; i++) {
+            char cur = s[i];
+            if (lastIndices[cur] < start) {
+                lastIndices[cur] = i;
+                curLen++;
+            } else {
+                int lastIndex = lastIndices[cur];
+                start = lastIndex + 1;
+                curLen = i - start + 1;
+                lastIndices[cur] = i;
+            }
+            if (curLen > maxLen) {
+                maxLen = curLen;
+            }
+        }
+        return maxLen;
+    }
+}
+```

LeetCodeNet/G0001_0100/S0004_median_of_two_sorted_arrays/readme.md

@@ -0,0 +1,90 @@
+[![](https://img.shields.io/github/stars/LeetCode-in-Net/LeetCode-in-Net?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net)
+[![](https://img.shields.io/github/forks/LeetCode-in-Net/LeetCode-in-Net?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net/fork)
+
+## 4\. Median of Two Sorted Arrays
+
+Hard
+
+Given two sorted arrays `nums1` and `nums2` of size `m` and `n` respectively, return **the median** of the two sorted arrays.
+
+The overall run time complexity should be `O(log (m+n))`.
+
+**Example 1:**
+
+**Input:** nums1 = [1,3], nums2 = [2]
+
+**Output:** 2.00000
+
+**Explanation:** merged array = [1,2,3] and median is 2. 
+
+**Example 2:**
+
+**Input:** nums1 = [1,2], nums2 = [3,4]
+
+**Output:** 2.50000
+
+**Explanation:** merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5. 
+
+**Example 3:**
+
+**Input:** nums1 = [0,0], nums2 = [0,0]
+
+**Output:** 0.00000 
+
+**Example 4:**
+
+**Input:** nums1 = [], nums2 = [1]
+
+**Output:** 1.00000 
+
+**Example 5:**
+
+**Input:** nums1 = [2], nums2 = []
+
+**Output:** 2.00000 
+
+**Constraints:**
+
+*   `nums1.length == m`
+*   `nums2.length == n`
+*   `0 <= m <= 1000`
+*   `0 <= n <= 1000`
+*   `1 <= m + n <= 2000`
+*   <code>-10<sup>6</sup> <= nums1[i], nums2[i] <= 10<sup>6</sup></code>
+
+## Solution
+
+```csharp
+public class Solution {
+    public double FindMedianSortedArrays(int[] nums1, int[] nums2) {
+        if (nums2.Length < nums1.Length) {
+            return FindMedianSortedArrays(nums2, nums1);
+        }
+        int cut1;
+        int cut2;
+        int n1 = nums1.Length;
+        int n2 = nums2.Length;
+        int low = 0;
+        int high = n1;
+        while (low <= high) {
+            cut1 = (low + high) / 2;
+            cut2 = ((n1 + n2 + 1) / 2) - cut1;
+            int l1 = cut1 == 0 ? int.MinValue : nums1[cut1 - 1];
+            int l2 = cut2 == 0 ? int.MinValue : nums2[cut2 - 1];
+            int r1 = cut1 == n1 ? int.MaxValue : nums1[cut1];
+            int r2 = cut2 == n2 ? int.MaxValue : nums2[cut2];
+            if (l1 <= r2 && l2 <= r1) {
+                if ((n1 + n2) % 2 == 0) {
+                    return (Math.Max(l1, l2) + Math.Min(r1, r2)) / 2.0;
+                }
+                return Math.Max(l1, l2);
+            } else if (l1 > r2) {
+                high = cut1 - 1;
+            } else {
+                low = cut1 + 1;
+            }
+        }
+        return 0.0;
+    }
+}
+```

LeetCodeNet/G0001_0100/S0005_longest_palindromic_substring/readme.md

@@ -0,0 +1,72 @@
+[![](https://img.shields.io/github/stars/LeetCode-in-Net/LeetCode-in-Net?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net)
+[![](https://img.shields.io/github/forks/LeetCode-in-Net/LeetCode-in-Net?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Net/LeetCode-in-Net/fork)
+
+## 5\. Longest Palindromic Substring
+
+Medium
+
+Given a string `s`, return _the longest palindromic substring_ in `s`.
+
+**Example 1:**
+
+**Input:** s = "babad"
+
+**Output:** "bab" **Note:** "aba" is also a valid answer. 
+
+**Example 2:**
+
+**Input:** s = "cbbd"
+
+**Output:** "bb" 
+
+**Example 3:**
+
+**Input:** s = "a"
+
+**Output:** "a" 
+
+**Example 4:**
+
+**Input:** s = "ac"
+
+**Output:** "a" 
+
+**Constraints:**
+
+*   `1 <= s.length <= 1000`
+*   `s` consist of only digits and English letters.
+
+## Solution
+
+```csharp
+public class Solution {
+    public string LongestPalindrome(string s) {
+        if (s.Length == 1) return s;
+        int res = 0;
+        int l = 0;
+        int r = 0;
+        int len = s.Length;
+        for (int i = 0; i < len; i ++) {
+            for (int diff = 1; i - diff + 1 >= 0 && i + diff < len; diff ++) {
+                if (s[i - diff + 1] != s[i + diff]) break;
+                else if (res < diff * 2) {
+                    res = diff * 2;
+                    l = i - diff + 1;
+                    r = i + diff;
+                }
+            }
+        }
+        for (int i = 0; i < len; i ++) {
+            for (int diff = 1; i - diff >= 0 && i + diff < len; diff ++) {
+                if (s[i - diff] != s[i + diff]) break;
+                else if (res < diff * 2 + 1) {
+                    res = diff * 2 + 1;
+                    l = i - diff;
+                    r = i + diff;
+                }
+            }
+        }
+        return s.Substring(l, r - l + 1);
+    }
+}
+```