Better table algorithm for visited table implementing a very simple hashset

chess_paths/chess_paths.c

@@ -255,20 +255,79 @@ unsigned int decreasing_path_len(const struct chessboard* c,
     return hops - 1;
 }
 
-void visit(bool* visited, unsigned columns, unsigned column, unsigned row) {
-    visited[column * columns + row] = true;
+struct row_list {
+    unsigned row;
+    unsigned column;
+    struct row_list* next;
+};
+
+typedef struct row_list* visit_table;
+unsigned long alloc = 0;
+
+unsigned long table_total_size(const struct chessboard*);
+unsigned long table_hash(const struct chessboard*, unsigned, unsigned);
+
+inline unsigned long table_total_size(const struct chessboard* c) {
+    return 100;
 }
 
-bool visited(bool* visited, unsigned columns, unsigned column, unsigned row) {
-    return visited[column * columns + row];
+inline unsigned long table_hash(const struct chessboard* c, unsigned col,
+        unsigned row) {
+    return (value_at(c, col, row) ^ 0xDEADBEEF) % table_total_size(c);
+}
+
+visit_table* table_new(const struct chessboard* c) {
+    unsigned long table_size = table_total_size(c);
+    alloc += sizeof(struct row_list*) * table_size;
+    return calloc(table_size, sizeof(struct row_list*));
+}
+
+void table_visit(const struct chessboard* c, visit_table* visited,
+        unsigned column, unsigned row) {
+
+    unsigned long hash = table_hash(c, column, row);
+    struct row_list* prev = hash[visited];
+    alloc += sizeof(struct row_list);
+    hash[visited] = malloc(sizeof(struct row_list));
+    assert(hash[visited] != NULL);
+    hash[visited]->row = row;
+    hash[visited]->column = column;
+    hash[visited]->next = prev;
+}
+
+bool table_visited(const struct chessboard* c, visit_table* visited,
+        unsigned column, unsigned row) {
+
+    unsigned long hash = table_hash(c, column, row);
+    for (struct row_list* i = hash[visited]; i != NULL; i = i->next) {
+        if (i->row == row && i->column == column) return true;
+    }
+    return false;
+}
+
+void table_destroy(const struct chessboard* c, visit_table* visited) {
+
+    unsigned long table_size = table_total_size(c);
+    for (unsigned e = 0; e < table_size; e++) {
+        for (struct row_list* i = e[visited], *j; i != NULL;) {
+            j = i->next;
+            free(i);
+            i = j;
+        }
+    }
+
+    printf("alloc = %lu\n", alloc);
+    alloc = 0;
+
+    free(visited);
 }
 
 unsigned int simple_path_len(const struct chessboard* c,
         struct piece_position* p) {
 
-    const unsigned int CC = columns(c);
-    bool* v = calloc(rows(c) * CC, sizeof(unsigned));
-    visit(v, CC, p->column, p->row);
+    visit_table* v = table_new(c);
+    table_visit(c, v, p->column, p->row);
+
 #if DEBUG
     print_visited(c, v);
 #endif
@@ -287,7 +346,7 @@ unsigned int simple_path_len(const struct chessboard* c,
 #endif
 
         while(poss != NULL) {
-            if (!visited(v, CC, poss->column, poss->row)) {
+            if (!table_visited(c, v, poss->column, poss->row)) {
                 next_v = value_at(c, poss->column, poss->row);
                 if (!has_next || next_v > base_v) {
                     has_next = true;
@@ -301,14 +360,14 @@ unsigned int simple_path_len(const struct chessboard* c,
             free(del);
         }
 
-        visit(v, CC, p->column, p->row);
+        table_visit(c, v, p->column, p->row);
 #if DEBUG
         print_visited(c, v);
 #endif
         hops++;
     }
 
-    free(v);
+    table_destroy(c, v);
     return hops - 1;
 }