/* [CHALLENGE] KNIGHT IS CALLING Write a program to print the amount of n-digit phone numbers that can be dialed by a chess knight on a 0-9 keypad that starts on any number and takes n-1 steps. For example: Input: 2 Output: 20 [04, 06, 16, 18, 27, 29, 34, 38, 43, 49, 40, 61, 67, 60, 72, 76, 81, 83, 92, 94] If the knight starts at 0 it can move to 4 or 6. If it starts at 1 it can move to 6 or 8, and so on. The keypad is of the form: 1 2 3 4 5 6 7 8 9 0 Don't use recursion. Input : Enter number <= 60 or press submit for default value of 8 Note: The Code requires C++17 or higher {} compiler */ #include #include using namespace std; using Row = valarray; auto cal_combos=[](auto ndig,auto ...Argsd){ // stores valid position of the knight move // starting from 0 to 9(inclusive) cells static const valarray LT{ {4,6},{8,6}, {7,9},{4,8},{3,9,0},{0},{1,7,0}, {2,6}, {1,3},{4,2}}; // starting row Row startc(1,10); // stores total number of combos size_t total_combo { startc.sum() }; for(int id{1}; id < ndig; ++id) { // new combo initialized to 0 Row nc(startc.size()); for(auto p : {0,1,2,3,4,6,7,8,9}) { auto pos = LT[p]; nc[pos] = Row(nc[pos]) + startc[p]; } total_combo = nc.sum(); // update the starting combo with the // newly calculated one startc = nc; } // end for cout << "Total combos for " << ndig << " digit Phone Number are " << total_combo << "\n\n"; if constexpr (sizeof ...(Argsd) > 0) { cal_combos(Argsd...); } }; int main() { int ndig{8}; cin >> ndig; if(ndig < 1) { cerr << "invalid phone digit length\n"; return 0; } // actual function to calculate combos cal_combos(ndig, 1, 2, 3, 4, 5, 8, 10, 17, 29, 42, 60); }

[Challenge] Knight_Dial.cpp