diff options
Diffstat (limited to 'knight_dialer.c')
-rw-r--r-- | knight_dialer.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/knight_dialer.c b/knight_dialer.c new file mode 100644 index 0000000..be72a6e --- /dev/null +++ b/knight_dialer.c @@ -0,0 +1,65 @@ +// 935. Knight Dialer +#include "leetcode.h" + +/* + * the chess knight has a unique movement, it may move two squares vertically + * and one square horizontally, or two squares horizontally andone square + * vertically with both forming the shape of an L. the possible movements of + * chess knights ares shown in below diagram. given an integer 'n', return how + * many distinct phone number of length 'n' we can dial. you are allowed to + * place the knight on any numeric cell initially and then you should perform 'n + * - 1' jumps to dial a number of length 'n'. all jumps should be valid jumps. + * as the answer may be very large, return answer modulo 10^9 + 7 + */ + +int knightDialer(int n) { + long int new_jump[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; + long int old_jump[] = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1}; + long long int numbers = 0; + int row0[] = {2, 4, 6}; + int row1[] = {2, 6, 8}; + int row2[] = {2, 7, 9}; + int row3[] = {2, 8, 4}; + int row4[] = {3, 3, 9, 0}; + int row5[] = {0}; + int row6[] = {3, 7, 0, 1}; + int row7[] = {2, 2, 6}; + int row8[] = {2, 1, 3}; + int row9[] = {2, 4, 2}; + int **dial = malloc(10 * sizeof(int *)); + dial[0] = row0; + dial[1] = row1; + dial[2] = row2; + dial[3] = row3; + dial[4] = row4; + dial[5] = row5; + dial[6] = row6; + dial[7] = row7; + dial[8] = row8; + dial[9] = row9; + if (n == 1) + return 10; + for (int i = 1; i < n; i++) { + numbers = 0; + for (int j = 0; j < 10; j++) + for (int k = 1; k < dial[j][0] + 1; k++) { + if (j == 5) + continue; + new_jump[dial[j][k]] += old_jump[j]; + new_jump[dial[j][k]] %= 1000000007LL; + } + memcpy(old_jump, new_jump, sizeof(long) * 10); + for (int j = 0; j < 10; j++) { + numbers += new_jump[j]; + new_jump[j] = 0; + } + } + free(dial); + return numbers % 1000000007LL; +} + +int main() { + printf("%d\n", knightDialer(1)); // expect: 10 + printf("%d\n", knightDialer(2)); // expect: 20 + printf("%d\n", knightDialer(3131)); // expect: 136006598 +} |