Euler krams

euler1.c

@@ -0,0 +1,13 @@
+#include <stdio.h>
+
+int numbersum(int i, int p) {
+    int n = p/i;
+    return i*n*(n+1)/2;
+}
+
+int main( int argc, char *argv[] ) {
+	int n = 999;
+    int s = numbersum(3,n) + numbersum(5,n) - numbersum(15,n);
+    printf("%d\n",s);
+	return 0;
+}

euler3.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <math.h>
+#include <assert.h>
+
+long max(long a, long b) {
+    return a > b ? a : b;
+}
+
+long largest_prime_factor(long n) {
+    int p = 2;
+    while(n > 1) {
+        while(p < n && n%p!=0) p++;
+        while(n%p==0) n/=p;
+    }
+    return p;
+}
+
+int main( int argc, char *argv[] ) {
+    assert(largest_prime_factor(13195) == 29);
+
+    printf("%d\n",largest_prime_factor(600851475143));
+
+	return 0;
+}

euler4.c

@@ -0,0 +1,49 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct palindrome_info {
+    int a;
+    int b;
+    int palindrome;
+};
+
+
+int makepalindrome(int n) {
+    int p = n*1000;
+    p += 100 * (n%10);
+    p += 10 * ((n/10)%10);
+    p += (n/100)%10;
+    return p;
+}
+
+struct palindrome_info* largestpalindrome() {
+    struct palindrome_info* info = malloc(sizeof(struct palindrome_info));
+    info->a = 0;
+    info->b = 0;
+    info->palindrome = 0;
+    int p,a;
+    for(int i = 999; i > 0; i--) {
+        p = makepalindrome(i);
+        a = 999;
+        while(a > 0 && p%a != 0) a--;
+        if(a > 0 && p/a < 1000) {
+            info->palindrome = p;
+            info->a = a;
+            info->b = p/a;
+            return info;
+        }
+    }
+    free(info);
+    return NULL;
+}
+
+int main( int argc, char *argv[] ) {
+    struct palindrome_info* info = largestpalindrome();
+    if(info != NULL) {
+        printf("A: %d\n",info->a);
+        printf("B: %d\n",info->b);
+        printf("Palindrom: %d\n",info->palindrome);
+        free(info);
+    }
+	return 0;
+}

euler5.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int ggT(int a, int b) {
+    if(a==0) return b;
+    while(b!=0) {
+        if(a > b) a -= b;
+        else b -= a;
+    }
+    return a;
+}
+
+int main( int argc, char *argv[] ) {
+	int n = 1;
+    for(int i = 20; i > 1; i--) {
+        if(n%i!=0) n*=i/ggT(i,n);
+    }
+
+    printf("%d\n",n);
+
+	return 0;
+}