Data commit

Task/Bell-numbers/C/bell-numbers.c

@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+// row starts with 1; col < row
+size_t bellIndex(int row, int col) {
+    return row * (row - 1) / 2 + col;
+}
+
+int getBell(int *bellTri, int row, int col) {
+    size_t index = bellIndex(row, col);
+    return bellTri[index];
+}
+
+void setBell(int *bellTri, int row, int col, int value) {
+    size_t index = bellIndex(row, col);
+    bellTri[index] = value;
+}
+
+int *bellTriangle(int n) {
+    size_t length = n * (n + 1) / 2;
+    int *tri = calloc(length, sizeof(int));
+    int i, j;
+
+    setBell(tri, 1, 0, 1);
+    for (i = 2; i <= n; ++i) {
+        setBell(tri, i, 0, getBell(tri, i - 1, i - 2));
+        for (j = 1; j < i; ++j) {
+            int value = getBell(tri, i, j - 1) + getBell(tri, i - 1, j - 1);
+            setBell(tri, i, j, value);
+        }
+    }
+
+    return tri;
+}
+
+int main() {
+    const int rows = 15;
+    int *bt = bellTriangle(rows);
+    int i, j;
+
+    printf("First fifteen Bell numbers:\n");
+    for (i = 1; i <= rows; ++i) {
+        printf("%2d: %d\n", i, getBell(bt, i, 0));
+    }
+
+    printf("\nThe first ten rows of Bell's triangle:\n");
+    for (i = 1; i <= 10; ++i) {
+        printf("%d", getBell(bt, i, 0));
+        for (j = 1; j < i; ++j) {
+            printf(", %d", getBell(bt, i, j));
+        }
+        printf("\n");
+    }
+
+    free(bt);
+    return 0;
+}