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#!/usr/bin/env cscript
/* SPDX-License-Identifier: GPL-2.0
*
* Copyright (C) 2018-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*/
#define _GNU_SOURCE
#include <stdint.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <errno.h>
enum { PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64 = 68 };
static inline size_t cord(size_t a, size_t b)
{
return a * (a + 1) / 2 + b;
}
static uint64_t *create_pascals_triangle(size_t num_rows)
{
uint64_t *triangle;
size_t i, j;
if (!num_rows || num_rows > PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64) {
errno = EINVAL;
return NULL;
}
triangle = reallocarray(NULL, cord(num_rows, 0), sizeof(*triangle));
if (!triangle)
return NULL;
for (i = 0; i < num_rows; ++i) {
triangle[cord(i, 0)] = triangle[cord(i, i)] = 1;
for (j = 1; j < i; ++j)
triangle[cord(i, j)] = triangle[cord(i - 1, j - 1)] + triangle[cord(i - 1, j)];
}
return triangle;
}
static void print_pascals_triangle(FILE *file, const uint64_t *triangle, size_t num_rows)
{
size_t i, j;
for (i = 0; i < num_rows; ++i) {
for (j = 0; j < i + 1; ++j)
fprintf(file, "%" PRIu64 " ", triangle[cord(i, j)]);
fputc('\n', file);
}
}
int main(int argc, char *argv[])
{
uint64_t *triangle;
size_t num_rows;
char *endptr;
if (argc != 2) {
fprintf(stderr, "Usage: %s ROWS\n", argv[0]);
return 1;
}
num_rows = strtoul(argv[1], &endptr, 10);
if (!*argv[1] || *endptr) {
fprintf(stderr, "ERROR: `%s' is not a valid number\n", argv[1]);
return 1;
}
triangle = create_pascals_triangle(num_rows);
if (!triangle) {
perror("ERROR: unable to create triangle");
return 1;
}
print_pascals_triangle(stdout, triangle, num_rows);
free(triangle);
return 0;
}
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