add: 231015

cpp/2308/LC231015.cpp

@@ -0,0 +1,23 @@
+#include "defs.h"
+#include <vector>
+
+constexpr static int MOD = 1'000'000'007;
+
+int LC231015::numWays(int steps, int arrLen) {
+	if (arrLen == 1)
+		return 1;
+	int n = std::min(arrLen, 505);
+	int ans[2][512] {{1}, {}};
+	for (int cs = 1; cs <= steps; ++cs) {
+		ans[cs & 1][0] = (ans[cs & 1 ^ 1][0] + ans[cs & 1 ^ 1][1]) % MOD;
+		for (int i = 1; i < n - 1; ++i)
+			ans[cs & 1][i] = (
+				(ans[cs & 1 ^ 1][i - 1] + ans[(cs & 1) ^ 1][i]) % MOD +
+				ans[cs & 1 ^ 1][i + 1]
+			) % MOD;
+		ans[cs & 1][n - 1] = (ans[cs & 1 ^ 1][n - 2] + ans[cs & 1 ^ 1][n - 1]) % MOD;
+	}
+	return ans[steps & 1][0];
+}
+
+using Solution = LC231015;

cpp/2308/defs.h

@@ -36,4 +36,9 @@ public:
 	static int paintWalls(const std::vector<int>&, const std::vector<int>&);
 };
 
+class LC231015 {
+public:
+	static int numWays(int, int);
+};
+
 #endif //LEETCODE_CPP_DEFS_H

cpp/2308/main.cpp

@@ -2,6 +2,6 @@
 #include <iostream>
 
 int main() {
-	std::cout << LC230927::decodeAtIndex("a2b3c4d5e6f7g8h9", 9);
+	std::cout << LC231015::numWays(4,2);
 	return 0;
 }