From cadb92b671d54d6c217e2a655e8e25f817105d6a Mon Sep 17 00:00:00 2001
From: Daniele Fucini <dfucini@gmail.com>
Date: Fri, 20 Sep 2019 15:12:47 +0200
Subject: [PATCH] Add solutions for problem 31

---
 C/p031.c       | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++
 Python/p030.py |  2 --
 Python/p031.py | 33 ++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+), 2 deletions(-)
 create mode 100644 C/p031.c
 create mode 100644 Python/p031.py

diff --git a/C/p031.c b/C/p031.c
new file mode 100644
index 0000000..41982ab
--- /dev/null
+++ b/C/p031.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+int count(int value, int n, int i);
+
+int coins[8] = {1, 2, 5, 10, 20, 50, 100, 200};
+
+int main(int argc, char **argv)
+{
+   int n;
+   double elapsed;
+   struct timespec start, end;
+
+   clock_gettime(CLOCK_MONOTONIC, &start);
+
+   n = count(0, 0, 0);
+
+   clock_gettime(CLOCK_MONOTONIC, &end);
+
+   elapsed = (end.tv_sec - start.tv_sec) + (double)(end.tv_nsec - start.tv_nsec) / 1000000000;
+
+   printf("Project Euler, Problem 31\n");
+   printf("Answer: %d\n", n);
+
+   printf("Elapsed time: %.9lf seconds\n", elapsed);
+
+   return 0;
+}
+
+int count(int value, int n, int i)
+{
+   int j;
+
+   for(j = i; j < 8; j++)
+   {
+      value += coins[j];
+
+      if(value == 200)
+      {
+         return n+1;
+      }
+      else if(value > 200)
+      {
+         return n;
+      }
+      else
+      {
+         n = count(value, n, j);
+         value -= coins[j];
+      }
+   }
+
+   return n;
+}
diff --git a/Python/p030.py b/Python/p030.py
index c86cba5..c0e86a1 100644
--- a/Python/p030.py
+++ b/Python/p030.py
@@ -1,7 +1,5 @@
 #!/usr/bin/python3
 
-from numpy import zeros
-
 from timeit import default_timer
 
 def main():
diff --git a/Python/p031.py b/Python/p031.py
new file mode 100644
index 0000000..c56f4e4
--- /dev/null
+++ b/Python/p031.py
@@ -0,0 +1,33 @@
+#!/usr/bin/python3
+
+from timeit import default_timer
+
+def count(coins, value, n, i):
+    for j in range(i, 8):
+        value = value + coins[j]
+        if value == 200:
+            return n + 1
+        elif value > 200:
+            return n
+        else:
+            n = count(coins, value, n, j)
+            value = value - coins[j]
+
+    return n
+
+def main():
+    start = default_timer()
+
+    coins = [1, 2, 5, 10, 20, 50, 100, 200]
+
+    n = count(coins, 0, 0, 0)
+
+    end = default_timer()
+
+    print('Project Euler, Problem 30')
+    print('Answer: {}'.format(n))
+
+    print('Elapsed time: {:.9f} seconds'.format(end - start))
+
+if __name__ == '__main__':
+    main()