Day 10 Add power function

Author: mandliya

README.md

@@ -6,8 +6,8 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 145 |
-| Current Streak | 9 days |
+| Total Problems | 146 |
+| Current Streak | 10 days |
 | Longest Streak | 91 ( August 17, 2015 - November 15, 2015 ) |
 
 </center>
@@ -146,6 +146,7 @@ Include contains single header implementation of data structures and some algori
 | Encrypt and then decrypts a text using Caeser Cipher. | [caeser_cipher.cpp](common_ds_algo_problems/caeser_cipher.cpp)|
 | Encrypt and then decrypts a text using Vigenère cipher. | [vigenere_cipher.cpp](common_ds_algo_problems/vigenere_cipher.cpp)|
 | Generate binary numbers between 1 to N efficiently. |[n_binary.cpp](common_ds_algo_problems/n_binary.cpp)|
+| Implement power function | [power_function.cpp](common_ds_algo_problems/power_function.cpp)|
 
 ### Math Problems
 | Problem | Solution |

common_ds_algo_problems/power_function.cpp

@@ -0,0 +1,45 @@
+/*
+ * Implement pow(a, b) function.
+ * We can recursively call a sub-problem
+ * if n is even, then pow(a,b) = pow(a, b/2) * pow(a, b/2);
+ * if n is odd then, pow(a, b) = a * pow(a, b/2) * pow(a, b/2);
+ */
+
+#include <iostream>
+
+int power(int a, int b)
+{
+    // base condition
+    //
+    if (b == 0)
+    {
+        return 1;
+    }
+
+    // sub-problem for this recursive call.
+    //
+    int p = power(a, b/2);
+
+    // if b is odd
+    if (b & 1)
+    {
+        return (a * p * p);
+    }
+    else
+    {
+        // if b is even
+        return (p * p);
+    }
+}
+
+int main()
+{
+    int a, b;
+    std::cout << "Calculating pow(a,b):\n";
+    std::cout << "Enter a:";
+    std::cin >> a;
+    std::cout << "Enter b:";
+    std::cin >> b;
+    std::cout << "pow(a,b) :" << power(a, b) << std::endl;
+ }
+