feat: add solution to lc problem: No.0034 (#4077)

Author: djvelimir

solution/0000-0099/0034.Find First and Last Position of Element in Sorted Array/README.md

@@ -211,6 +211,31 @@ var searchRange = function (nums, target) {
 };
 ```
 
+#### C#
+
+```cs
+public class Solution {
+    public int[] SearchRange(int[] nums, int target) {
+        int l = Search(nums, target);
+        int r = Search(nums, target + 1);
+        return l == r ? new int[] {-1, -1} : new int[] {l, r - 1};
+    }
+
+    private int Search(int[] nums, int x) {
+        int left = 0, right = nums.Length;
+        while (left < right) {
+            int mid = (left + right) >>> 1;
+            if (nums[mid] >= x) {
+                right = mid;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left;
+    }
+}
+```
+
 #### PHP
 
 ```php

solution/0000-0099/0034.Find First and Last Position of Element in Sorted Array/README_EN.md

@@ -201,6 +201,31 @@ var searchRange = function (nums, target) {
 };
 ```
 
+#### C#
+
+```cs
+public class Solution {
+    public int[] SearchRange(int[] nums, int target) {
+        int l = Search(nums, target);
+        int r = Search(nums, target + 1);
+        return l == r ? new int[] {-1, -1} : new int[] {l, r - 1};
+    }
+
+    private int Search(int[] nums, int x) {
+        int left = 0, right = nums.Length;
+        while (left < right) {
+            int mid = (left + right) >>> 1;
+            if (nums[mid] >= x) {
+                right = mid;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left;
+    }
+}
+```
+
 #### PHP
 
 ```php

solution/0000-0099/0034.Find First and Last Position of Element in Sorted Array/Solution.cs

@@ -0,0 +1,20 @@
+public class Solution {
+    public int[] SearchRange(int[] nums, int target) {
+        int l = Search(nums, target);
+        int r = Search(nums, target + 1);
+        return l == r ? new int[] {-1, -1} : new int[] {l, r - 1};
+    }
+
+    private int Search(int[] nums, int x) {
+        int left = 0, right = nums.Length;
+        while (left < right) {
+            int mid = (left + right) >>> 1;
+            if (nums[mid] >= x) {
+                right = mid;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left;
+    }
+}