Add binary search

Author: rp-code9

Diff for: README.md

@@ -176,6 +176,10 @@ Princeton Algorithms [Part 1](https://www.coursera.org/learn/algorithms-part1/)
     * Using max heap [C++](problems/sorting/KthLargest.cpp)
     * Using STL iterator and algorithm [C++](problems/sorting/KthLargest.cpp)
     * Using quick select algorithm [C++](problems/sorting/QuickSelect.cpp)
+* Binary Search
+    * Iterative [C++](problems/searching/BinarySearch.cpp)
+    * Recursive [C++](problems/searching/BinarySearch.cpp)
+    * C++ STL [C++](problems/searching/BinarySearch.cpp)
 
 ## Dynamic Programming
 * Word Break problem

Diff for: problems/searching/BinarySearch.cpp

@@ -0,0 +1,84 @@
+// Binary search recursive and iterative
+// Techie delight https://www.techiedelight.com/binary-search/
+
+#include <iostream>
+#include <vector>
+#include <cstdlib>
+#include <algorithm>
+
+void print(const std::vector<int>& nums)
+{
+    for (auto n : nums) {
+        std::cout << n << " ";
+    }
+    std::cout << "\n";
+}
+
+std::vector<int> generateRandomNumbers(const int length, const int min, const int max)
+{
+    std::vector<int> nums;
+    for (int i = 0; i < length; ++i) {
+        int x = min + (rand() % max - min + 1);
+        nums.push_back(x);
+    }
+    return nums;
+}
+
+int searchIterative(std::vector<int>& nums, const int target)
+{
+    int low = 0;
+    int high = nums.size() - 1;
+
+    while (low <= high) {
+        int mid = low + (high - low) / 2;
+        if (nums[mid] == target) {
+            return mid;
+        } else if (target < nums[mid]) {
+            high = mid - 1;
+        } else {
+            low = mid + 1;
+        }
+    }
+
+    return -1;
+}
+
+int searchRecursive(std::vector<int>& nums, const int target, int low, int high)
+{
+    if (low > high) {
+        return -1;
+    }
+    int mid = low + (high - low) / 2;
+    if (nums[mid] == target) {
+        return mid;
+    } else if (target < nums[mid]) {
+        return searchRecursive(nums, target, low, mid - 1);
+    } else {
+        return searchRecursive(nums, target, mid + 1, high);
+    }
+}
+
+int searchRecursive(std::vector<int>& nums, const int target)
+{
+    return searchRecursive(nums, target, 0, nums.size() - 1);
+}
+
+void test(std::vector<int>& nums, const int target)
+{
+    std::cout << "Numbers : ";
+    print(nums);
+    std::sort(nums.begin(), nums.end(), std::less<int>());
+    std::cout << "\nSearching "<< target << " using iterative : Found at " << searchIterative(nums, target);
+    std::cout << "\nSearching "<< target << " using recursive : Found at " << searchRecursive(nums, target);
+    std::cout << "\nSearching "<< target << " using STL : Found? " << std::boolalpha
+                << std::binary_search(nums.begin(), nums.end(), target);
+    std::cout << "\n";
+}
+
+int main()
+{
+    std::vector<int> nums = generateRandomNumbers(50, 1, 50);
+    test(nums, 5);
+
+    return 0;
+}