new solution

Author: shreymehul

415.AddStrings.cs

@@ -0,0 +1,50 @@
+// 415. Add Strings
+// Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 
+// as a string.
+// You must solve the problem without using any built-in library for handling large integers 
+// (such as BigInteger). You must also not convert the inputs to integers directly.
+
+// Example 1:
+// Input: num1 = "11", num2 = "123"
+// Output: "134"
+// Example 2:
+// Input: num1 = "456", num2 = "77"
+// Output: "533"
+// Example 3:
+// Input: num1 = "0", num2 = "0"
+// Output: "0"
+
+// Constraints:
+// 1 <= num1.length, num2.length <= 104
+// num1 and num2 consist of only digits.
+// num1 and num2 don't have any leading zeros except for the zero itself.
+
+
+//Not working for long long inputs
+public class Solution {
+    public string AddStrings(string num1, string num2) {
+        return (long.Parse(num1) + long.Parse(num2)).ToString();
+    }
+}
+
+public class Solution {
+    public string AddStrings(string num1, string num2) {
+         StringBuilder result = new StringBuilder();
+        int carry = 0;
+        int p1 = num1.Length - 1;
+        int p2 = num2.Length - 1;
+        while (p1 >= 0 || p2 >= 0) {
+            int x1 = p1 >= 0 ? num1[p1] - '0' : 0;
+            int x2 = p2 >= 0 ? num2[p2] - '0' : 0;
+            int sum = x1 + x2 + carry;
+            result.Insert(0, sum % 10);
+            carry = sum / 10;
+            p1--;
+            p2--;
+        }
+        if (carry > 0) {
+            result.Insert(0, carry);
+        }
+        return result.ToString();
+    }
+}

452.FindMinArrowShots.cs

@@ -24,6 +24,11 @@
 // -231 <= xstart < xend <= 231 - 1
 
 
+//The intuition behind the solution is to sort the intervals (balloons) by their end points. 
+// Then, iterate through the sorted list and shoot an arrow at the end point of the current balloon. 
+// This arrow will also burst all other balloons whose start point is less than or equal to the current
+// balloon's end point. 
+// This is because the sorted order ensures that all such balloons will overlap with the current balloon.
 public class Solution {
     public int FindMinArrowShots(int[][] points) {
         points = points.OrderBy(x => x[1]).ThenBy(x => x[0]).ToArray();

482.LicenseKeyFormatting.cs

@@ -0,0 +1,55 @@
+// 482. License Key Formatting
+// You are given a license key represented as a string s that consists of only alphanumeric characters 
+// and dashes. The string is separated into n + 1 groups by n dashes. You are also given an integer k.
+
+// We want to reformat the string s such that each group contains exactly k characters, 
+// except for the first group, which could be shorter than k but still must contain at least one character. 
+// Furthermore, there must be a dash inserted between two groups, and you should convert all lowercase letters to uppercase.
+
+// Return the reformatted license key.
+
+// Example 1:
+// Input: s = "5F3Z-2e-9-w", k = 4
+// Output: "5F3Z-2E9W"
+// Explanation: The string s has been split into two parts, each part has 4 characters.
+// Note that the two extra dashes are not needed and can be removed.
+// Example 2:
+// Input: s = "2-5g-3-J", k = 2
+// Output: "2-5G-3J"
+// Explanation: The string s has been split into three parts, each part has 2 characters except the first part as it could be shorter as mentioned above.
+
+// Constraints:
+// 1 <= s.length <= 105
+// s consists of English letters, digits, and dashes '-'.
+// // 1 <= k <= 104
+
+public class Solution {
+    public string LicenseKeyFormatting(string s, int k) {
+        s = s.Replace("-", "").ToUpper();
+        //intution: insert '-' from the end of the string with k interval.
+        var sb = new StringBuilder(s);
+        for(int i = s.Length - k; i > 0; i -= k){
+            sb.Insert(i, '-');
+        }
+        return sb.ToString();
+    }
+}
+
+
+public class Solution {
+    public string LicenseKeyFormatting(string s, int k) {
+        
+        s = s.Replace("-", "").ToUpper();
+        string res = "";
+        for(int i = s.Length; i >= 0; i -= k){
+            string temp = "";
+            for(int j = Math.Max(i - k, 0); j < i; j++ ){
+                temp += s[j];
+            }
+            res = temp + res;
+            if(i - k > 0)
+                res = "-" + res;
+        }
+        return res;
+    }
+}

541.ReverseStr.cs

@@ -0,0 +1,37 @@
+// 541. Reverse String II
+// Given a string s and an integer k, reverse the first k characters for every 2k characters counting 
+// from the start of the string.
+
+// If there are fewer than k characters left, reverse all of them. 
+// If there are less than 2k but greater than or equal to k characters, then reverse the first k 
+// characters and leave the other as original.
+
+// Example 1:
+// Input: s = "abcdefg", k = 2
+// Output: "bacdfeg"
+// Example 2:
+// Input: s = "abcd", k = 2
+// Output: "bacd"
+ 
+// Constraints:
+// 1 <= s.length <= 104
+// s consists of only lowercase English letters.
+// 1 <= k <= 104
+
+public class Solution {
+    public string ReverseStr(string s, int k) {
+        char[] arr = s.ToCharArray();
+        //intution: reverse the first k characters for every 2k characters counting from the start of the string.
+        //incrementing i by 2*k because we need to reverse the first k characters for every 2k characters
+        for (int i = 0; i < arr.Length; i += 2 * k) {
+            int left = i;
+            int right = Math.Min(i + k - 1, arr.Length - 1);
+            while (left < right) {
+                (arr[left], arr[right]) = ((arr[right], arr[left]));
+                left++;
+                right--;
+            }
+        }
+        return new string(arr);
+    }
+}