From 957aa0c0c95335f8f5b962c4c6739b0544710e3b Mon Sep 17 00:00:00 2001
From: Al <albarrentine@gmail.com>
Date: Mon, 3 Apr 2017 00:15:31 -0400
Subject: [PATCH] [utils] cartesian product iterator for grid search during
 model selection

---
 src/cartesian_product.c | 91 +++++++++++++++++++++++++++++++++++++++++
 src/cartesian_product.h | 23 +++++++++++
 2 files changed, 114 insertions(+)
 create mode 100644 src/cartesian_product.c
 create mode 100644 src/cartesian_product.h

diff --git a/src/cartesian_product.c b/src/cartesian_product.c
new file mode 100644
index 00000000..fa57e778
--- /dev/null
+++ b/src/cartesian_product.c
@@ -0,0 +1,91 @@
+#include "cartesian_product.h"
+#include <stdarg.h>
+
+cartesian_product_iterator_t *cartesian_product_iterator_new_vargs(size_t n, va_list args) {
+    cartesian_product_iterator_t *iter = malloc(sizeof(cartesian_product_iterator_t));
+    if (iter == NULL) return NULL;
+
+    iter->lengths = uint32_array_new_size(n);
+    if (iter->lengths == NULL) {
+        goto exit_iter_created;
+    }
+
+    size_t remaining = 1;
+    for (size_t i = 0; i < n; i++) {
+        uint32_t arg = va_arg(args, uint32_t);
+        uint32_array_push(iter->lengths, arg);
+        if (arg > 0) {
+            remaining *= arg;
+        }
+    }
+    iter->remaining = remaining;
+
+    iter->state = uint32_array_new_zeros(n);
+    if (iter->state == NULL) {
+        goto exit_iter_created;
+    }
+
+    return iter;
+
+exit_iter_created:
+    cartesian_product_iterator_destroy(iter);
+    return NULL;
+}
+
+cartesian_product_iterator_t *cartesian_product_iterator_new(size_t n, ...) {
+    va_list args;
+    va_start(args, n);
+    cartesian_product_iterator_t *iter = cartesian_product_iterator_new_vargs(n, args);
+    va_end(args);
+    return iter;
+}
+
+uint32_t *cartesian_product_iterator_start(cartesian_product_iterator_t *self) {
+    return self->state->a;
+}
+
+bool cartesian_product_iterator_done(cartesian_product_iterator_t *self) {
+    return self->remaining == 0;
+}
+
+uint32_t *cartesian_product_iterator_next(cartesian_product_iterator_t *self) {
+    if (self == NULL) return NULL;
+
+    uint32_t *lengths = self->lengths->a;
+    uint32_t *state = self->state->a;
+
+    if (self->remaining > 0) {
+        ssize_t i;
+        ssize_t n = self->lengths->n;
+        for (i = n - 1; i >= 0; i--) {
+            state[i]++;
+            if (state[i] == lengths[i]) {
+                state[i] = 0;
+            } else {
+                self->remaining--;
+                break;
+            }
+        }
+        if (i < 0) {
+            self->remaining = 0;
+        }
+    } else {
+        return NULL;
+    }
+
+    return state;
+}
+
+void cartesian_product_iterator_destroy(cartesian_product_iterator_t *self) {
+    if (self == NULL) return;
+
+    if (self->lengths != NULL) {
+        uint32_array_destroy(self->lengths);
+    }
+
+    if (self->state != NULL) {
+        uint32_array_destroy(self->state);
+    }
+
+    free(self);
+}
diff --git a/src/cartesian_product.h b/src/cartesian_product.h
new file mode 100644
index 00000000..d38917fd
--- /dev/null
+++ b/src/cartesian_product.h
@@ -0,0 +1,23 @@
+#ifndef CARTESIAN_PRODUCT_H
+#define CARTESIAN_PRODUCT_H
+
+#include <stdlib.h>
+#include <stdarg.h>
+
+#include "collections.h"
+
+typedef struct cartesian_product_iterator {
+    size_t remaining;
+    uint32_array *lengths;
+    uint32_array *state;
+} cartesian_product_iterator_t;
+
+cartesian_product_iterator_t *cartesian_product_iterator_new(size_t n, ...);
+cartesian_product_iterator_t *cartesian_product_iterator_new_vargs(size_t n, va_list args);
+uint32_t *cartesian_product_iterator_start(cartesian_product_iterator_t *self);
+uint32_t *cartesian_product_iterator_next(cartesian_product_iterator_t *self);
+bool cartesian_product_iterator_done(cartesian_product_iterator_t *self);
+
+void cartesian_product_iterator_destroy(cartesian_product_iterator_t *self);
+
+#endif
\ No newline at end of file