3 files changed, 92 insertions, 0 deletions
diff --git a/challenge-175/walt-mankowski/c/Makefile b/challenge-175/walt-mankowski/c/Makefile
new file mode 100644
index 0000000000..d1cec8a239
--- /dev/null
+++ b/challenge-175/walt-mankowski/c/Makefile
@@ -0,0 +1,18 @@
+C = /usr/bin/cc
+CFLAGS = -Wall -O3
+
+all: ch-1 ch-2
+
+%.o: %.cpp
+	$(CPP) $(CPPFLAGS) -c $<
+
+ch-1: ch-1.o
+	$(C) -o $@ ch-1.o
+
+ch-2: ch-2.o
+	$(C) -o $@ ch-2.o
+
+clean:
+	rm -f *~
+	rm -f *.o
+	rm -f ch-1 ch-2
diff --git a/challenge-175/walt-mankowski/c/ch-1.c b/challenge-175/walt-mankowski/c/ch-1.c
new file mode 100644
index 0000000000..346c8fdb0b
--- /dev/null
+++ b/challenge-175/walt-mankowski/c/ch-1.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+const bool is_leap_year(const int year) {
+    if (year % 4)
+        return false;
+    else if (year % 100)
+        return true;
+    else if (year % 400)
+        return false;
+    else
+        return true;
+}
+
+int main(int argc, char *argv[]) {
+    const int days_in_month[2][12] = {
+        { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
+        { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
+    };
+
+    const int year = atoi(argv[1]);
+    const int leap = is_leap_year(year);
+    for (int month = 0; month < 12; month++) {
+        struct tm ts;
+        memset(&ts, 0, sizeof(ts));
+        ts.tm_mon = month;
+        ts.tm_year = year - 1900;
+        ts.tm_mday = days_in_month[leap][month];
+        ts.tm_isdst = -1;
+        mktime(&ts);
+        printf("%d-%02d-%2d\n", ts.tm_year + 1900, month+1, ts.tm_mday - ts.tm_wday);
+    }
+}
diff --git a/challenge-175/walt-mankowski/c/ch-2.c b/challenge-175/walt-mankowski/c/ch-2.c
new file mode 100644
index 0000000000..81d217dc81
--- /dev/null
+++ b/challenge-175/walt-mankowski/c/ch-2.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+const int gcd(const int a, const int b) {
+    return b ? gcd(b, a % b) : a;
+}
+
+int main(int argc, char *argv[]) {
+    const int MAX = 6000;
+    int *totient = calloc(MAX, sizeof(int));
+
+    for (int n = 2; n <= MAX; n++)
+        for (int i = 1; i <= n-1; i++)
+            if (gcd(n, i) == 1)
+                totient[n]++;
+
+    int perfect[20];
+    int i = 2;
+    int n = 0;
+    while (n < 20 && i < 6000) {
+        int tot = totient[i];
+        int sum = tot;
+        while (tot != 1) {
+            if (sum > i)
+                break;
+            else {
+                tot = totient[tot];
+                sum += tot;
+            }
+        }
+        if (sum == i)
+            perfect[n++] = i;
+        i++;
+    }
+    for (int i = 0; i < 20; i++)
+        printf("%d ", perfect[i]);
+    printf("\n");
+}