add: 221020-CN

cpp/2210/221020-CN.cpp

@@ -0,0 +1,30 @@
+#include <cstdio>
+
+/**
+ * 779. K-th Symbol in Grammar
+ * We build a table of n rows (1-indexed). We start by writing 0 in the 1st row. Now in every subsequent row, we look at the previous row and replace each occurrence of 0 with 01, and each occurrence of 1 with 10.
+ * - For example, for n = 3, the 1st row is 0, the 2nd row is 01, and the 3rd row is 0110.
+ * Given two integer n and k, return the kth (1-indexed) symbol in the nth row of a table of n rows.
+ */
+
+class Solution {
+public:
+    static int kthGrammar(int n, int k) {
+        --k;
+        int cur = 0;
+        while (--n)
+            cur ^= !!(k & (1 << (n - 1)));
+        return cur;
+    }
+};
+
+int main() {
+    std::printf("%d\n", Solution::kthGrammar(1, 1));
+    std::printf("%d\n", Solution::kthGrammar(2, 1));
+    std::printf("%d\n", Solution::kthGrammar(2, 2));
+    std::printf("%d\n", Solution::kthGrammar(3, 1));
+    std::printf("%d\n", Solution::kthGrammar(3, 2));
+    std::printf("%d\n", Solution::kthGrammar(3, 3));
+    std::printf("%d\n", Solution::kthGrammar(3, 4));
+    return 0;
+}

cpp/2210/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2210)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2210 221019.cpp)
+ADD_EXECUTABLE(2210 221020-CN.cpp)