Merge pull request #858 from notauserx/Create-287-Find-the-Duplicate-Number.cs

Create 287-Find-the-Duplicate-Number.cs

Author: Ahmad-A0

Diff for: csharp/287-Find-the-Duplicate-Number.cs

@@ -0,0 +1,38 @@
+public class Solution {
+    public int FindDuplicate(int[] nums) {
+        return floydAlgorithm(nums);
+        // return arrayAsHashMapIterative(nums);
+    }
+    
+    private int floydAlgorithm(int[] nums) {
+        int slow = 0, fast = 0;
+        
+        while(true) {
+            slow = nums[slow];
+            fast = nums[nums[fast]];
+            if (slow == fast)
+                break;
+        }
+        
+        var slow2 = 0;
+        
+        while(true) {
+            slow = nums[slow];
+            slow2 = nums[slow2];
+            if (slow == slow2)
+                return slow;
+        }
+        
+        return 0;
+    }
+    
+    private int arrayAsHashMapIterative(int[] nums) {
+        while(nums[0] != nums[nums[0]]) {
+            int nxt = nums[nums[0]];
+            nums[nums[0]] = nums[0];
+            nums[0] = nxt;
+        }
+        
+        return nums[0];
+    }
+}