problems(cpp): add “935. Knight Dialer”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/cpp/knight-dialer.cpp

@@ -0,0 +1,76 @@
+#include <array>
+#include <cstdint>
+#include <numeric>
+#include <vector>
+
+class Solution {
+    using pad_t = std::array<int, 12>;
+
+    static bool isValidMove(int i) {
+        return i >= 0 && i < 12 && i != 9 && i != 11;
+    }
+
+    static int index(int x, int y) {
+        if (x < 0 || x >= 3 || y < 0 || y >= 4) {
+            return -1;
+        }
+
+        return y * 3 + x;
+    }
+
+    static int add(int x, int y) { return (x + y) % 1000000007; }
+
+    static int get(const std::vector<pad_t>& dp, int it, int idx) {
+        if (it < 0 || it >= static_cast<int>(dp.size())) {
+            return 0;
+        }
+
+        if (!isValidMove(idx)) {
+            return 0;
+        }
+
+        return dp[it][idx];
+    }
+
+    static void dpIteration(std::vector<pad_t>& dp, int it) {
+        for (int i = 0; i < 12; ++i) {
+            if (!isValidMove(i)) {
+                continue;
+            }
+
+            int dx = -2, dy = -1;
+            for (int j = 0; j < 8; ++j) {
+                auto next = index(i % 3 + dx, i / 3 + dy);
+                dp[it][i] = add(dp[it][i], get(dp, it - 1, next));
+
+                // adjustment of the dx, dy
+                dy *= -1;
+
+                if (j % 2 == 1) {
+                    dx *= -1;
+                }
+
+                if (j % 4 == 3) {
+                    int d = dx;
+                    dx = dy;
+                    dy = d;
+                }
+            }
+        }
+    }
+
+   public:
+    int knightDialer(int n) {
+        std::vector<pad_t> dp(n);
+
+        dp[0].fill(1);
+        dp[0][9] = 0;
+        dp[0][11] = 0;
+
+        for (int i = 1; i < n; ++i) {
+            dpIteration(dp, i);
+        }
+
+        return std::accumulate(dp.back().begin(), dp.back().end(), 0, add);
+    }
+};