Find peak element (#194)

* add find peak element

* impl find peak element

leetcode-cc/FindPeakElement.hpp

@@ -0,0 +1,54 @@
+#include <algorithm>
+
+#include "TestHelper.h"
+#include "problem.h"
+#include "solution.h"
+
+using namespace std;
+
+IMPLEMENT_PROBLEM_CLASS(PFindPeakElement, 162, DIFFI_MEDIUM, TOPIC_ALGORITHMS,
+                        "Find Peak Element", "", {""});
+
+class SFindPeakElement : public ISolution {
+ public:
+  size_t problemId() const override { return 162; }
+  string name() const override {
+    return ("Solution for " + string("Find Peak Element"));
+  }
+  string location() const override { return __FILE_NAME__; }
+  int test() const override {
+    return testHelper<vector<int>, int>(
+        {{1, 2, 3, 1}, {1, 2, 1, 3, 5, 6, 4}}, {2, 1},
+        [this](auto input) { return this->findPeakElement(input); });
+  };
+  int benchmark() const override { return 0; }
+
+ private:
+  int findPeakElement(vector<int>& nums) const {
+    int n = nums.size();
+    if (n == 1) return 0;
+    if (n == 2) return nums[0] < nums[1] ? 1 : 0;
+
+    if (nums[0] > nums[1]) {
+      return 0;
+    }
+
+    int prev = 0;
+    int current = 1;
+    int next = 2;
+
+    while (next <= n) {
+      if (next == n) {
+        return nums[prev] < nums[current] ? current : prev;
+      } else if (nums[prev] < nums[current] && nums[next] < nums[current]) {
+        return current;
+      } else {
+        prev++;
+        current++;
+        next++;
+      }
+    }
+
+    return -1;
+  }
+};

runtime-cc/src/registration.cc

@@ -23,6 +23,7 @@
 #include "../leetcode-cc/EvaluateReversePolishNotation.hpp"
 #include "../leetcode-cc/FindMinInRotatedSortedArray.hpp"
 #include "../leetcode-cc/FindMinInRotatedSortedArrayII.hpp"
+#include "../leetcode-cc/FindPeakElement.hpp"
 #include "../leetcode-cc/FindPlayersWithZeroOrOneLosses.hpp"
 #include "../leetcode-cc/FlattenBTreeToLinkedList.hpp"
 #include "../leetcode-cc/FourSum.hpp"
@@ -693,5 +694,10 @@ const int registerAll(std::shared_ptr<Container> handle) {
   handle->registerSolution(
       []() -> ArcSolution { return std::make_shared<SIntersectionOfTwoLL>(); });
 
+  handle->registerProblem(
+      []() -> ArcProblem { return std::make_shared<PFindPeakElement>(); });
+  handle->registerSolution(
+      []() -> ArcSolution { return std::make_shared<SFindPeakElement>(); });
+
   return 0;
 }