add: 220109

2201/220109.cpp

@@ -0,0 +1,56 @@
+#include <string>
+#include <iostream>
+
+/**
+ * 1041. Robot Bounded In Circle
+ * On an infinite plane, a robot initially stands at (0, 0) and faces north. The robot can receive one of three instructions:
+ * "G": go straight 1 unit;
+ * "L": turn 90 degrees to the left;
+ * "R": turn 90 degrees to the right.
+ * The robot performs the instructions given in order, and repeats them forever.
+ * Return true if and only if there exists a circle in the plane such that the robot never leaves the circle.
+ */
+
+class Solution {
+private:
+	// N, E, S, W
+	inline static int dX[4] = {0, 1, 0, -1};
+	inline static int dY[4] = {1, 0, -1, 0};
+public:
+	static bool isRobotBounded(std::string instructions) {
+		// instructions = instructions * 8;
+		instructions.append(instructions);
+		instructions.append(instructions);
+		instructions.append(instructions);
+
+		int l = instructions.length();
+		int X = 0, Y = 0, D = 0;
+		const char* const str = instructions.c_str();
+		for (int i = 0; i < l; ++i) {
+			switch (str[i]) {
+				case 'G':
+					X += dX[D];
+					Y += dY[D];
+					break;
+				case 'L':
+					D = (D + 3) % 4;
+					break;
+				case 'R':
+					D = (D + 1) % 4;
+					break;
+				default:
+					; // Should never reach here.
+			}
+			if (!X && !Y && !D && !std::strncmp(str, str + i + 1, i + 1)) {
+				return true;
+			}
+		}
+		return false;
+	}
+};
+
+int main() {
+	bool ans = Solution::isRobotBounded("GL");
+	std::cout << ans;
+	return 0;
+}

2201/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2201)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2201 220109-CN.cpp)
+ADD_EXECUTABLE(2201 220109.cpp)