p17

p17.c

@@ -0,0 +1,90 @@
+
+/*
+ * http://projecteuler.net
+ *
+ * Projecteuler - Problem 17
+ * ------------------------
+ * 2011-02-03 Henrik Hautakoski
+ */
+
+#include <stdio.h>
+
+#define N_AND 3
+#define N_HUNDRED 7
+#define N_THOUSAND 8
+
+int len_ones(int n) {
+
+    switch(n) {
+    case 1: case 2: case 6:
+        return 3;
+    case 4: case 5: case 9:
+        return 4;
+    case 3: case 7: case 8:
+        return 5;
+    }
+    return 0;
+}
+
+int len_tentwenty(int n) {
+
+    switch(n) {
+    case 1: case 2:
+        return 6;
+    case 5: case 6:
+        return 7;
+    case 3: case 4: case 8: case 9:
+        return 8;
+    case 7:
+        return 9;
+    }
+    return 0;
+}
+
+int len_tens(int n) {
+
+    switch(n) {
+    case 1:
+        return 3;
+    case 4: case 5: case 6:
+        return 5;
+    case 2: case 3: case 8: case 9:
+        return 6;
+    case 7:
+        return 7;
+    }
+    return 0;
+}
+
+int len(int n) {
+
+    int ret = 0;
+
+    if (n > 99) {
+        ret += len_ones(n / 100);
+        n = n % 100;
+        if (n)
+            ret += N_AND;
+        ret += N_HUNDRED;
+    }
+
+    if (n > 10 && n < 20) {
+        ret += len_tentwenty(n % 10);
+    } else {
+        ret += len_ones(n % 10);
+        ret += len_tens(n / 10);
+    }
+    return ret;
+}
+
+int main() {
+
+    int i, n = len_ones(1) + N_THOUSAND;
+
+    for(i=1; i < 1000; i++)
+        n += len(i);
+
+    printf("%i\n", n);
+
+    return 0;
+}