// 840. Magic Squares In Grid #include "leetcode.h" /* * a 3 * 3 magic square is a 3 x 3 grid filled with distinct numbers from 1 to 9 * such that each row, column, and both diagonals all have the same sum. given a * row x col 'grid' of integers, how many 3 x 3 contiguous magic square subgrids * are there? note, while a magic square can only contain numbers from 1 to 9, * 'grid' may contain numbers up to 15. */ bool check(int **grid, int row, int col, int *map) { for (int i = 0; i < 3; i++) for (int j = 0; j < 3; j++) { map[grid[row + i][col + j]]++; if (map[grid[row + i][col + j]] > 1 || grid[row + i][col + j] > 9 || grid[row + i][col + j] == 0) return false; } int a = grid[row][col] + grid[row][col + 1] + grid[row][col + 2]; int b = grid[row + 1][col] + grid[row + 1][col + 1] + grid[row + 1][col + 2]; int c = grid[row + 2][col] + grid[row + 2][col + 1] + grid[row + 2][col + 2]; if (a != 15 || b != 15 || c != 15) return false; int d = grid[row][col] + grid[row + 1][col] + grid[row + 2][col]; int e = grid[row][col + 1] + grid[row + 1][col + 1] + grid[row + 2][col + 1]; int f = grid[row][col + 2] + grid[row + 1][col + 2] + grid[row + 2][col + 2]; if (d != 15 || e != 15 || f != 15) return false; int g = grid[row][col] + grid[row + 1][col + 1] + grid[row + 2][col + 2]; int h = grid[row][col + 2] + grid[row + 1][col + 1] + grid[row + 2][col]; if (g != 15 || h != 15) return false; return true; } int numMagicSquaresInside(int **grid, int gridSize, int *gridColSize) { if (gridSize < 3 || gridColSize[0] < 3) return 0; int *map = (int *)calloc(16, sizeof(int)), cnt = 0; for (int i = 0; i + 2 < gridSize; i++) for (int j = 0; j + 2 < gridColSize[0]; j++) { if (check(grid, i, j, map)) cnt++; memset(map, 0, 16 * sizeof(int)); } free(map); return cnt; } int main() { int g1[3][4] = {{4, 3, 8, 4}, {9, 5, 1, 9}, {2, 7, 6, 2}}, g2[1][1] = {{8}}, gcs1 = 3, gcs2 = 1; printf("%d\n", numMagicSquaresInside((int **)g1, ARRAY_SIZE(g1), &gcs1)); // expect: 1 printf("%d\n", numMagicSquaresInside((int **)g2, ARRAY_SIZE(g2), &gcs2)); // expect: 0 }