Data commit

Task/Sphenic-numbers/C/sphenic-numbers.c

@@ -0,0 +1,129 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <math.h>
+#include <locale.h>
+
+bool *sieve(int limit) {
+    int i, p;
+    limit++;
+    // True denotes composite, false denotes prime.
+    bool *c = calloc(limit, sizeof(bool)); // all false by default
+    c[0] = true;
+    c[1] = true;
+    for (i = 4; i < limit; i += 2) c[i] = true;
+    p = 3; // Start from 3.
+    while (true) {
+        int p2 = p * p;
+        if (p2 >= limit) break;
+        for (i = p2; i < limit; i += 2 * p) c[i] = true;
+        while (true) {
+            p += 2;
+            if (!c[p]) break;
+        }
+    }
+    return c;
+}
+
+void primeFactors(int n, int *factors, int *length) {
+    if (n < 2) return;
+    int count = 0;
+    int inc[8] = {4, 2, 4, 2, 4, 6, 2, 6};
+    while (!(n%2)) {
+        factors[count++] = 2;
+        n /= 2;
+    }
+    while (!(n%3)) {
+        factors[count++] = 3;
+        n /= 3;
+    }
+    while (!(n%5)) {
+        factors[count++] = 5;
+        n /= 5;
+    }
+    for (int k = 7, i = 0; k*k <= n; ) {
+        if (!(n%k)) {
+            factors[count++] = k;
+            n /= k;
+        } else {
+            k += inc[i];
+            i = (i + 1) % 8;
+        }
+    }
+    if (n > 1) {
+        factors[count++] = n;
+    }
+    *length = count;
+}
+
+int compare(const void* a, const void* b) {
+    int arg1 = *(const int*)a;
+    int arg2 = *(const int*)b;
+    if (arg1 < arg2) return -1;
+    if (arg1 > arg2) return 1;
+    return 0;
+}
+
+int main() {
+    const int limit = 1000000;
+    int limit2 = (int)cbrt((double)limit);
+    int i, j, k, pc = 0, count = 0, prod, res;
+    bool *c = sieve(limit/6);
+    for (i = 0; i < limit/6; ++i) {
+        if (!c[i]) ++pc;
+    }
+    int *primes = (int *)malloc(pc * sizeof(int));
+    for (i = 0, j = 0; i < limit/6; ++i) {
+        if (!c[i]) primes[j++] = i;
+    }
+    int *sphenic = (int *)malloc(210000 * sizeof(int));
+    printf("Sphenic numbers less than 1,000:\n");
+    for (i = 0; i < pc-2; ++i) {
+        if (primes[i] > limit2) break;
+        for (j = i+1; j < pc-1; ++j) {
+            prod = primes[i] * primes[j];
+            if (prod * primes[j+1] >= limit) break;
+            for (k = j+1; k < pc; ++k) {
+                res = prod * primes[k];
+                if (res >= limit) break;
+                sphenic[count++] = res;
+            }
+        }
+    }
+    qsort(sphenic, count, sizeof(int), compare);
+    for (i = 0; ; ++i) {
+        if (sphenic[i] >= 1000) break;
+        printf("%3d ", sphenic[i]);
+        if (!((i+1) % 15)) printf("\n");
+    }
+    printf("\nSphenic triplets less than 10,000:\n");
+    int tripCount = 0, s, t = 0;
+    for (i = 0; i < count - 2; ++i) {
+        s = sphenic[i];
+        if (sphenic[i+1] == s+1 && sphenic[i+2] == s+2) {
+            tripCount++;
+            if (s < 9998) {
+                printf("[%d, %d, %d] ", s, s+1, s+2);
+                if (!(tripCount % 3)) printf("\n");
+            }
+            if (tripCount == 5000) t = s;
+        }
+    }
+    setlocale(LC_NUMERIC, "");
+    printf("\nThere are %'d sphenic numbers less than 1,000,000.\n", count);
+    printf("There are %'d sphenic triplets less than 1,000,000.\n", tripCount);
+    s = sphenic[199999];
+    int factors[10], length = 0;
+    primeFactors(s, factors, &length);
+    printf("The 200,000th sphenic number is %'d (", s);
+    for (i = 0; i < length; ++i) {
+        printf("%d", factors[i]);
+        if (i < length-1) printf("*");
+    }
+    printf(").\n");
+    printf("The 5,000th sphenic triplet is [%d, %d, %d].\n", t, t+1, t+2);
+    free(c);
+    free(primes);
+    free(sphenic);
+    return 0;
+}