old stuff: algorithms

1 files changed, 63 insertions, 0 deletions

diff --git a/algorithms/magic_coxeter.c b/algorithms/magic_coxeter.c
new file mode 100644
index 0000000..17d24f6
--- /dev/null
+++ b/algorithms/magic_coxeter.c
@@ -0,0 +1,63 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+
+void
+magic(unsigned int n)
+{
+  int m[n*n];
+
+  unsigned int i;
+  for (i=0; i<n*n; i++) {
+    m[i] = 0;
+  }
+
+  int z, pos=n/2, npos;
+  for (z=1; z<=n*n; z++) {
+    m[pos] = z;
+    if(pos%n == 0) {
+      if(pos == 0) {
+        npos = n*n-1;
+      } else {
+        npos = pos-1;
+      }
+    } else {
+      if(pos-n-1 < 0) {
+        npos = (n*n-1) - abs(n-pos);
+      } else {
+        npos = pos-n-1;
+      }
+    }
+    if(m[npos] != 0) {
+      npos = pos+n;
+    }
+    pos = npos;
+  }
+
+  unsigned int j;
+  for(j=0; j<n*n; j++) {
+    printf("\t%d\t",m[j]);
+    if((j+1)%n==0 && j!=0) {
+      printf("\n");
+    }
+  }
+}
+
+int
+main(int argc, char **argv)
+{
+  if(argc!=2) {
+    printf("Usage: %s <n>\n", argv[0]);
+    exit(1);
+  }
+  int n = atoi(argv[1]);
+  if(n%2==0) {
+    printf("n has to be odd\n");
+    exit(1);
+  }
+  magic(n);
+
+  return 0;
+}
+