Problem 60 (prime pairs)

eu060.c

@@ -0,0 +1,49 @@
+#include "euler.h"
+
+static int primes[100000];
+static int length;
+
+static int prime_pair(int a, int b) {
+  char string[50];
+  int n;
+
+  sprintf(string, "%d%d", primes[a], primes[b]);
+  n = atoi(string);
+  if (!is_prime(n)) return 0;
+
+  sprintf(string, "%d%d", primes[b], primes[a]);
+  n = atoi(string);
+  if (!is_prime(n)) return 0;
+
+  return 1;
+}
+
+void eu060(char *ans) {
+  length = genprimes(primes, 10000);
+
+  int a, b, c, d, e;
+
+  for (a = 0; a <= length-5; a++) {
+    for (b = a; b <= length-4; b++) {
+      if (!prime_pair(a, b)) continue;
+      for (c = b; c <= length-3; c++) {
+        if (!prime_pair(a, c)) continue;
+        if (!prime_pair(b, c)) continue;
+        for (d = c; d <= length-2; d++) {
+          if (!prime_pair(a, d)) continue;
+          if (!prime_pair(b, d)) continue;
+          if (!prime_pair(c, d)) continue;
+
+          for (e = d; e <= length-1; e++) {
+            if (!prime_pair(a, e)) continue;
+            if (!prime_pair(b, e)) continue;
+            if (!prime_pair(c, e)) continue;
+            if (!prime_pair(d, e)) continue;
+            sprintf(ans, "%d", primes[a] + primes[b] + primes[c] + primes[d] + primes[e]);
+            return;
+          }
+        }
+      }
+    }
+  }
+}

euler.c

@@ -236,6 +236,7 @@ struct puzzle puzzles[] = {
   { "057", &eu057, "153" },
   { "058", &eu058, "26241" },
   { "059", &eu059, "107359" },
+  { "060", &eu060, NULL },
 };
 
 #define NPUZZLES (sizeof puzzles / sizeof(puzzles[0]))