Merge pull request #54 from Liam0205/10_recursive

[C++][10_recursive] 课程中上台阶代码实现

c-cpp/10_recursive/one_two_step.cc

@@ -0,0 +1,71 @@
+#include <iostream>
+#include <unordered_map>
+
+class SolutionOFOneTwoStep {
+  private:
+    static std::unordered_map<size_t, size_t> result_;
+
+  public:
+    enum class POLICY {
+        RECURSIVE,
+        NONRECURSIVE
+    };
+
+  private:
+    size_t recursive(size_t steps) {
+        auto iter = result_.find(steps);
+        if (result_.end() != iter) {  // found.
+            return iter->second;
+        } else {
+            size_t res = operator()(steps - 1) + operator()(steps - 2);
+            result_.insert({steps, res});
+            return res;
+        }
+    }
+    size_t nonrecursive(size_t steps) {
+        auto iter = result_.find(steps);
+        if (result_.end() != iter) {  // found.
+            return iter->second;
+        } else {
+            size_t start;
+            for (start = steps; start != 2 and result_.end() == result_.find(start); --start) {}
+            for (size_t i = start; i != steps; ++i) {
+                result_.insert({i + 1, result_[i - 1] + result_[i]});
+            }
+            return result_[steps];
+        }
+    }
+
+  public:
+    size_t operator()(size_t steps, const POLICY policy = POLICY::RECURSIVE) {
+        if (policy == POLICY::RECURSIVE) {
+            return recursive(steps);
+        } else if (policy == POLICY::NONRECURSIVE) {
+            return nonrecursive(steps);
+        }
+    }
+    static void debug() {
+        for (auto kv : result_) {
+            std::cout << kv.first << ' ' << kv.second << std::endl;
+        }
+        std::cout << std::endl;
+    }
+};
+
+std::unordered_map<size_t, size_t> SolutionOFOneTwoStep::result_ = {{1, 1}, {2, 2}};
+
+int main() {
+    SolutionOFOneTwoStep::debug();
+
+    std::cout << SolutionOFOneTwoStep()(5, SolutionOFOneTwoStep::POLICY::RECURSIVE) << std::endl;
+    SolutionOFOneTwoStep::debug();
+
+    std::cout << SolutionOFOneTwoStep()(10, SolutionOFOneTwoStep::POLICY::NONRECURSIVE) << std::endl;
+    SolutionOFOneTwoStep::debug();
+
+    std::cout << SolutionOFOneTwoStep()(20, SolutionOFOneTwoStep::POLICY::RECURSIVE) << std::endl;
+    SolutionOFOneTwoStep::debug();
+
+    return 0;
+}
+