Data commit

Task/Descending-primes/AWK/descending-primes.awk

@@ -0,0 +1,35 @@
+# syntax: GAWK -f DESCENDING_PRIMES.AWK
+BEGIN {
+    start = 1
+    stop = 99999999
+    for (i=start; i<=stop; i++) {
+      leng = length(i)
+      flag = 1
+      for (j=1; j<leng; j++) {
+        if (substr(i,j,1) <= substr(i,j+1,1)) {
+          flag = 0
+          break
+        }
+      }
+      if (flag) {
+        if (is_prime(i)) {
+          printf("%9d%1s",i,++count%10?"":"\n")
+        }
+      }
+    }
+    printf("\n%d-%d: %d descending primes\n",start,stop,count)
+    exit(0)
+}
+function is_prime(n,  d) {
+    d = 5
+    if (n < 2) { return(0) }
+    if (n % 2 == 0) { return(n == 2) }
+    if (n % 3 == 0) { return(n == 3) }
+    while (d*d <= n) {
+      if (n % d == 0) { return(0) }
+      d += 2
+      if (n % d == 0) { return(0) }
+      d += 4
+    }
+    return(1)
+}