Initial data commit

Task/Prime-triangle/C/prime-triangle-1.c

@@ -0,0 +1,84 @@
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <time.h>
+
+bool is_prime(unsigned int n) {
+    assert(n < 64);
+    static bool isprime[] = {0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0,
+                             0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1,
+                             0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1,
+                             0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0};
+    return isprime[n];
+}
+
+void swap(unsigned int* a, size_t i, size_t j) {
+    unsigned int tmp = a[i];
+    a[i] = a[j];
+    a[j] = tmp;
+}
+
+bool prime_triangle_row(unsigned int* a, size_t length) {
+    if (length == 2)
+        return is_prime(a[0] + a[1]);
+    for (size_t i = 1; i + 1 < length; i += 2) {
+        if (is_prime(a[0] + a[i])) {
+            swap(a, i, 1);
+            if (prime_triangle_row(a + 1, length - 1))
+                return true;
+            swap(a, i, 1);
+        }
+    }
+    return false;
+}
+
+int prime_triangle_count(unsigned int* a, size_t length) {
+    int count = 0;
+    if (length == 2) {
+        if (is_prime(a[0] + a[1]))
+            ++count;
+    } else {
+        for (size_t i = 1; i + 1 < length; i += 2) {
+            if (is_prime(a[0] + a[i])) {
+                swap(a, i, 1);
+                count += prime_triangle_count(a + 1, length - 1);
+                swap(a, i, 1);
+            }
+        }
+    }
+    return count;
+}
+
+void print(unsigned int* a, size_t length) {
+    if (length == 0)
+        return;
+    printf("%2u", a[0]);
+    for (size_t i = 1; i < length; ++i)
+        printf(" %2u", a[i]);
+    printf("\n");
+}
+
+int main() {
+    clock_t start = clock();
+    for (unsigned int n = 2; n < 21; ++n) {
+        unsigned int a[n];
+        for (unsigned int i = 0; i < n; ++i)
+            a[i] = i + 1;
+        if (prime_triangle_row(a, n))
+            print(a, n);
+    }
+    printf("\n");
+    for (unsigned int n = 2; n < 21; ++n) {
+        unsigned int a[n];
+        for (unsigned int i = 0; i < n; ++i)
+            a[i] = i + 1;
+        if (n > 2)
+            printf(" ");
+        printf("%d", prime_triangle_count(a, n));
+    }
+    printf("\n");
+    clock_t end = clock();
+    double duration = (end - start + 0.0) / CLOCKS_PER_SEC;
+    printf("\nElapsed time: %f seconds\n", duration);
+    return 0;
+}

Task/Prime-triangle/C/prime-triangle-2.c

@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <stdint.h>
+
+#define GCC_ASM // use GCC's asm for i386. If it does not work, #undef it to use alternative func
+typedef uint32_t uint;
+typedef uint64_t ulong;
+
+#define MASK 0xa08228828228a2bULL
+
+#ifdef GCC_ASM
+
+static inline uint
+bpos(uint x)
+{
+	uint b;
+	asm("bsf %0, %0" : "=r" (b): "0" (x));
+	return b;
+}
+
+#else
+
+static inline uint
+bpos(uint x)
+{
+	static const uint bruijin[32] = {
+		 0,  1, 28,  2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17,  4, 8,
+		31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18,  6, 11,  5, 10, 9
+	};
+	return bruijin[((uint)((x & -x) * 0x077CB531U)) >> 27];
+}
+
+#endif // GCC_ASM
+
+int count(uint n, const uint s, uint avail)
+{
+	int cnt = 0;
+
+	avail ^= s;
+	if (--n)
+		for (uint b = (uint)(MASK>>bpos(s)) & avail; b; b &= b-1)
+			cnt += count(n, b&-b, avail);
+	else
+		return (MASK & s) != 0;
+
+	return cnt;
+}
+
+int disp(uint n, const uint s, uint avail, int maxn, uint *seq)
+{
+	seq[n--] = s;
+	if (!n) {
+		if ((MASK & s)) {
+			for (int i = 0; i < maxn; i++)
+				printf(" %d", bpos(seq[i]) + 1);
+			putchar('\n');
+			return 1;
+		}
+	} else {
+		for (uint b = (uint)(MASK>>bpos(s)) & (avail ^= s); b; b &= b-1)
+			if (disp(n, b&-b, avail, maxn, seq))
+				return 1;
+	}
+	return 0;
+}
+
+int chain(uint n, int count_only)
+{
+	const uint top = 1U<<(n - 1);
+	const uint avail = 2*top - 2;
+
+	if (count_only)
+		return count(n - 1, top, avail);
+
+	uint seq[32];
+	seq[0] = 1;
+	disp(n - 1, top, avail, n, seq);
+
+	return 0;
+}
+
+int main(void)
+{
+	for (int n = 2; n < 21; n++)
+		chain(n, 0);
+	putchar('\n');
+
+	for (int n = 2; n < 21; n++)
+		printf("%d ", chain(n, 1));
+	putchar('\n');
+
+	return 0;
+}