init p1 to p9

p4.c

@@ -0,0 +1,58 @@
+
+/*
+ * http://projecteuler.net
+ * 
+ * Projecteuler - Problem 4
+ * ------------------------
+ * 2009-12-28 Henrik Hautakoski
+ * 
+ * A somewhat elegant solution (representing the numbers as a string is not so fancy)
+ */
+
+#include <stdio.h>
+
+int factor(int val) {
+	
+	int a;
+	
+	for(a=999; a > 99; a--) {
+		
+		if((val % a) == 0 && (val/a) < 999)
+			return a;
+	}
+	
+	return 0;
+}
+
+int ispalindrom(int num) {
+	
+	int i, n;
+	char buffer[7];
+	
+	sprintf(buffer, "%i", num);
+	for(n=0; buffer[n+1] != 0; n++);
+	
+	for(i=0; i < n-i; i++) {
+		
+		if (buffer[i] != buffer[n-i])
+			return 0;
+	}
+	
+	return 1;
+}
+
+int main() {
+	
+	int r, a;
+	
+	for(r=999999; r >= 100001; r--) {
+		
+		if (!ispalindrom(r) || !(a = factor(r)))
+			continue;
+		
+		printf("%i * %i = %i\n", r/a, a, r);
+		break;
+	}
+	
+	return 0;
+}