2 files changed, 132 insertions, 0 deletions
diff --git a/c/wip/053-combinatoric-selections.c b/c/wip/053-combinatoric-selections.c
new file mode 100644
index 0000000..9006f5a
--- /dev/null
+++ b/c/wip/053-combinatoric-selections.c
@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+
+typedef long long unsigned int Natural;
+
+Natural factorial(Natural n)
+{
+    if (n == 1 || n == 0) return 1;
+    else return n * factorial(n - 1);
+}
+
+Natural combination(Natural n, Natural r)
+{
+    if (r > n) exit(1);
+    Natural num = 0;
+    /* for (Natural i = 0; i < r - 1; i++) */
+    /*     num *= n - i; */
+    /* return num / factorial(r); */
+    /* if (factorial(r) * factorial(n - r) == 0) return 0; */
+    return (factorial(n) / (factorial(r) * factorial(n - r)));
+    /* return  (factorial(r) * factorial(n - r)); */
+}
+
+int main(void)
+{
+    printf("10! = %llu\n", factorial(10));
+    printf("23! = %llu\n", factorial(23));
+    printf("(23 - 10)! = %llu\n", factorial(23 - 10));
+    int counter = 0;
+    Natural comb = 0, n, r;
+    /* for (n = 1; n <= 24; n++) */
+    /*     for (r = 1; r <= n; r++) { */
+    /*         comb = combination(n, r); */
+    /*         if (comb > 1000000) { */
+    /*             counter++; */
+    /* comb = combination(23, 10); */
+                printf("%llu C %llu = %llu\n", n, r, comb);
+            /* } */
+        /* } */
+    printf("counter = %d", counter);
+    return 0;
+}
diff --git a/c/wip/092-square_digit_chains.c b/c/wip/092-square_digit_chains.c
new file mode 100644
index 0000000..7029ccd
--- /dev/null
+++ b/c/wip/092-square_digit_chains.c
@@ -0,0 +1,89 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <math.h>
+
+
+int lenHelper(int x)
+{
+    if (x >= 10000000)   return 8;
+    if (x >= 1000000)    return 7;
+    if (x >= 100000)     return 6;
+    if (x >= 10000)      return 5;
+    if (x >= 1000)       return 4;
+    if (x >= 100)        return 3;
+    if (x >= 10)         return 2;
+    return 1;
+}
+
+int get_digit(int nb, int digit_index)
+{
+    if (digit_index == 1)
+        return nb % 10;
+    
+    return (int)(nb / pow(10.0, (double)(digit_index-1))) % 10;
+}
+
+int next_iteration(int nb)
+{
+    int i, sum = 0;
+    for (i = 0; i < lenHelper(nb); i++) {
+        sum += pow(get_digit(nb, i), 2);
+    }
+    return sum;
+}
+
+bool end_of_square_digit_chain_is_89(int nb)
+{
+    bool once = false;
+    int next_nb;
+    for (int i = 0; i < 10; i++) {
+        // printf("%d", next_nb);
+        next_nb  = next_iteration(nb);
+        if (next_nb == 89 || next_nb == 1) {
+            if (once) {
+                return next_nb == 89 ? true : false;
+            }
+            once = true;
+        }
+        nb = next_nb;
+    }
+    return false;
+}
+
+
+int main(void)
+{
+    int i, counter = 0;
+    for (i = 1; i < 10000000; i++) {
+        // printf("%d\n", i);
+        if (end_of_square_digit_chain_is_89(i))
+            counter++;
+            if (i % 1000000 == 0)
+                printf("%d\n", counter);
+    }
+
+    printf("%d\n", counter);
+
+    return 0;
+}
+
+
+
+// def end_of_square_digit_chain_is_89(nb):
+//     once = False
+//     while True:
+//         next_nb = sum([int(x)**2 for x in str(nb)])
+//         if next_nb == 89 or next_nb == 1:
+//             if once:
+//                 return True if next_nb == 89 else False
+//             once = True
+//         nb = next_nb
+
+// counter = 0
+// for i in range(1, 10_000_000):
+//     if end_of_square_digit_chain_is_89(i):
+//         counter += 1
+//         if i % 1000_000 == 0:
+//             print(counter)
+//             pass
+// print(counter)