rename repo, subdir for yearly challenges

2020/day09/ex1-c.c

@@ -0,0 +1,103 @@
+/* ex1-c: Advent2020 game, day 9/game 1
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct list {
+    unsigned size;
+    unsigned last;
+    unsigned long long *list;
+};
+
+#define DEFNSUM		25
+#define BLOCKSIZE	1024    /* number of elements for realloc() */
+
+void print_list(list)
+    struct list *list;
+{
+    unsigned i, psize=list->last;
+    unsigned long long *ptr=list->list;
+
+    fprintf(stderr, "PROGRAM: address=%p pinstr=%p size=%d\n", list, ptr, psize);
+    for (i=0; i<psize; ++i)
+        printf("[%u] %llu\n", i, *(ptr+i));
+}
+
+static struct list *add_line(list, line)
+    struct list *list;
+    char *line;
+{
+    int val;
+    unsigned cur, size;
+    unsigned long long *ptr;
+
+    if (!list) {
+        list=malloc(sizeof(struct list));
+        list->list=malloc(sizeof(unsigned long long)*BLOCKSIZE);
+        list->size=BLOCKSIZE;
+        list->last=0;
+    }
+    cur=list->last;
+    size=list->size;
+
+    if (cur == size) {
+        size+=BLOCKSIZE;
+        list->size=size;
+        list->list=realloc(list->list, sizeof(unsigned long long)*size);
+        fprintf(stderr, "realloc buf: cur=%d size=%d ptr=%p\n", cur, size, list->list);
+    }
+    ptr=list->list+cur;
+
+    sscanf(line, "%d", &val);
+    *ptr=val;
+    list->last++;
+
+    return list;
+}
+
+unsigned long long calc(list, cur, nsum)
+    struct list *list;
+    int cur;
+    unsigned nsum;
+{
+    unsigned long long *ptr=list->list;
+    unsigned long long res=*(ptr+cur);
+    int start=cur-nsum, i, j;
+
+    for (i=start; i<cur; ++i) {
+        for (j=i+1; j<cur; ++j) {
+            if (ptr[i]+ptr[j] == res)
+                return 0;
+        }
+    }
+    return res;
+}
+
+int main(ac, av)
+    int ac;
+    char **av;
+{
+    unsigned nsum=DEFNSUM;
+    char line[80];
+    struct list *list=NULL;
+    unsigned i;
+    unsigned long long res;
+
+    if (ac==2) {
+        nsum=atoi(*(av+1));
+    }
+
+    while (fgets(line, sizeof line, stdin)) {
+        list=add_line(list, line);
+    }
+    //print_list(list);
+    for (i=nsum; i<list->last; ++i) {
+        if (res=calc(list, i, nsum)) {
+            printf("%s : res=%llu\n", *av, res);
+            break;
+        }
+    }
+    exit (0);
+}