cpp: add «150. Evaluate Reverse Polish Notation»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/evaluate-reverse-polish-notation.cpp

@@ -0,0 +1,57 @@
+#include <cassert>
+#include <functional>
+#include <string>
+#include <vector>
+
+class Solution {
+    static auto get_function(const std::string &op)
+        -> std::function<int(int, int)> {
+        if (op == "+") {
+            return std::plus<int>{};
+        } else if (op == "-") {
+            return std::minus<int>{};
+        } else if (op == "*") {
+            return std::multiplies<int>{};
+        } else if (op == "/") {
+            return std::divides<int>{};
+        }
+
+        assert(false);
+    }
+
+  public:
+    auto evalRPN(const std::vector<std::string> &tokens) -> int {
+        std::vector<int> stack;
+
+        for (const auto &token : tokens) {
+            if (token == "+" || token == "-" || token == "*" || token == "/") {
+                assert(stack.size() >= 2);
+
+                int right = stack.back();
+                stack.pop_back();
+                int left = stack.back();
+                stack.pop_back();
+
+                stack.push_back(get_function(token)(left, right));
+            } else {
+                stack.push_back(std::stoi(token));
+            }
+        }
+
+        return stack.back();
+    }
+};
+
+int main() {
+    Solution s;
+
+    assert(s.evalRPN(std::vector<std::string>{
+               {"2"}, {"1"}, {"+"}, {"3"}, {"*"}}) == 9);
+    assert(s.evalRPN(std::vector<std::string>{
+               {"4"}, {"13"}, {"5"}, {"/"}, {"+"}}) == 6);
+    assert(s.evalRPN(std::vector<std::string>{{"10", "6", "9", "3", "+", "-11",
+                                               "*", "/", "*", "17", "+", "5",
+                                               "+"}}) == 22);
+
+    return 0;
+}