day 4

CMakeLists.txt

@@ -5,4 +5,5 @@ set(CMAKE_C_STANDARD 99)
 
 add_executable(day1 day1.c)
 add_executable(day2 day2.c)
-add_executable(day3 day3.c)
+add_executable(day3 day3.c)
+add_executable(day4 day4.c)

day4.c

@@ -0,0 +1,41 @@
+//
+// Created by red on 04/12/19.
+//
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+int power(int base, int pow){
+  if (pow <= 0) return 1;
+  return base*power(base,pow-1);
+}
+
+int main(){
+  const int lower = 152085;
+  const int upper = 670283;
+  int digits[6];
+  int ctr = 0;
+  for (size_t i = lower; i <= upper; i++){
+    for (size_t j = 0; j < 6; j++) {
+      int mult = power(10, j);
+      digits[j] = ((int) i % (10*mult)) / mult;
+    }
+    bool dd = false;
+    bool increasing = true;
+    int run = 1;
+    for (size_t j = 1; j < 6; j++) {
+      if (digits[j] == digits[j-1]) run++;
+      else {
+        if (run == 2) dd = true;
+        run = 1;
+      }
+      if (digits[j] > digits[j-1]) increasing = false;
+    }
+    if (run == 2) dd = true;
+    if (dd && increasing) ctr++;
+  }
+  printf("%d numbers found\n", ctr);
+  return EXIT_SUCCESS;
+}
+