Add minimax (#517)

* Add minimax

* Rename Backtracking/minimax.cpp to backtracking/minimax.cpp

* Wrap a long line

backtracking/minimax.cpp

@@ -0,0 +1,27 @@
+#include <cmath>
+#include <iostream>
+#include <vector>
+
+using std::cout;
+using std::endl;
+using std::max;
+using std::min;
+using std::vector;
+
+int minimax(int depth, int node_index, bool is_max, vector<int> scores,
+            int height) {
+    if (depth == height)
+        return scores[node_index];
+
+    int v1 = minimax(depth + 1, node_index * 2, !is_max, scores, height);
+    int v2 = minimax(depth + 1, node_index * 2 + 1, !is_max, scores, height);
+
+    return is_max ? max(v1, v2) : min(v1, v2);
+}
+
+int main() {
+    vector<int> scores = { 90, 23, 6, 33, 21, 65, 123, 34423 };
+    int height = log2(scores.size());
+
+    cout << "Optimal value: " << minimax(0, 0, true, scores, height) << endl;
+}