Added homework for algorithms complexity

DSA/01. Algorithms Complexity/README.md

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+## Data Structures, Algorithms and Complexity Homework
+
+1. **What is the expected running time of the following C# code?**
+  - Explain why using Markdown.
+  - Assume the array's size is `n`.
+
+  ```cs
+  long Compute(int[] arr)
+  {
+      long count = 0;
+      for (int i=0; i<arr.Length; i++)
+      {
+          int start = 0, end = arr.Length-1;
+          while (start < end)
+              if (arr[start] < arr[end])
+                  { start++; count++; }
+              else
+                  end--;
+      }
+      return count;
+  }
+  ```
+The expected running time of the algorithm is **~n*(n-1)** because the outer *for* loop will execute **n** number of times and the inner *while* loop will execute another maximum of **n-1** times. Complexity is **O(n^2)**
+
+2. **What is the expected running time of the following C# code?**
+  - Explain why using Markdown.
+  - Assume the input matrix has size of `n * m`.
+
+  ```cs
+  long CalcCount(int[,] matrix)
+  {
+      long count = 0;
+      for (int row=0; row<matrix.GetLength(0); row++)
+          if (matrix[row, 0] % 2 == 0)
+              for (int col=0; col<matrix.GetLength(1); col++)
+                  if (matrix[row,col] > 0)
+                      count++;
+      return count;
+  }
+  ```
+The expected running time of this algorithm is **n*m**. It will iterate **n** times for each row and then another **m** times for each column in the current row.
+
+3. **(*) What is the expected running time of the following C# code?**
+  - Explain why using Markdown.
+  - Assume the input matrix has size of `n * m`.
+
+  ```cs
+  long CalcSum(int[,] matrix, int row)
+  {
+      long sum = 0;
+      for (int col = 0; col < matrix.GetLength(0); col++)
+          sum += matrix[row, col];
+      if (row + 1 < matrix.GetLength(1))
+          sum += CalcSum(matrix, row + 1);
+      return sum;
+  }
+
+  Console.WriteLine(CalcSum(matrix, 0));
+  ```