diff --git a/solutions/1072. Flip Columns For Maximum Number of Equal Rows/1072.cs b/solutions/1072. Flip Columns For Maximum Number of Equal Rows/1072.cs
new file mode 100644
index 0000000..e4b43b2
--- /dev/null
+++ b/solutions/1072. Flip Columns For Maximum Number of Equal Rows/1072.cs	
@@ -0,0 +1,49 @@
+public class Solution
+{
+    public int MaxEqualRowsAfterFlips(int[][] matrix)
+    {
+        int m = matrix.Length;
+        int n = matrix[0].Length;
+        int ans = 0;
+        int[] flip = new int[n];
+        HashSet<int> seen = new HashSet<int>();
+
+        for (int i = 0; i < m; ++i)
+        {
+            if (seen.Contains(i))
+                continue;
+
+            int count = 0;
+
+            for (int j = 0; j < n; ++j)
+                flip[j] = 1 ^ matrix[i][j];
+
+            for (int k = 0; k < m; ++k)
+            {
+                if (AreArraysEqual(matrix[k], matrix[i]) || AreArraysEqual(matrix[k], flip))
+                {
+                    seen.Add(k);
+                    ++count;
+                }
+            }
+
+            ans = Math.Max(ans, count);
+        }
+
+        return ans;
+    }
+
+    private bool AreArraysEqual(int[] a, int[] b)
+    {
+        if (a.Length != b.Length) 
+            return false;
+
+        for (int i = 0; i < a.Length; i++)
+        {
+            if (a[i] != b[i]) 
+                return false;
+        }
+        
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/solutions/400. Nth Digit/400.cs b/solutions/400. Nth Digit/400.cs
new file mode 100644
index 0000000..4418f75
--- /dev/null
+++ b/solutions/400. Nth Digit/400.cs	
@@ -0,0 +1,21 @@
+public class Solution
+{
+    public int FindNthDigit(int n)
+    {
+        int digitSize = 1;
+        int startNum = 1;
+        long count = 9;
+
+        while (digitSize * count < n)
+        {
+            n -= digitSize * (int)count;
+            ++digitSize;
+            startNum *= 10;
+            count *= 10;
+        }
+
+        int targetNum = startNum + (n - 1) / digitSize;
+        int index = (n - 1) % digitSize;
+        return (int)(targetNum.ToString()[index]) - '0';
+    }
+}
\ No newline at end of file