From 4e6f7e55af1cb63f27d49f56d9568df72f11aa8f Mon Sep 17 00:00:00 2001
From: "exercism-solutions-syncer[bot]"
 <211797793+exercism-solutions-syncer[bot]@users.noreply.github.com>
Date: Mon, 19 Jan 2026 17:48:20 +0000
Subject: [PATCH] [Sync Iteration] c/react/1

---
 solutions/c/react/1/react.c | 289 ++++++++++++++++++++++++++++++++++++
 solutions/c/react/1/react.h |  29 ++++
 2 files changed, 318 insertions(+)
 create mode 100644 solutions/c/react/1/react.c
 create mode 100644 solutions/c/react/1/react.h

diff --git a/solutions/c/react/1/react.c b/solutions/c/react/1/react.c
new file mode 100644
index 0000000..1272afd
--- /dev/null
+++ b/solutions/c/react/1/react.c
@@ -0,0 +1,289 @@
+#include "react.h"
+#include <assert.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct cell_node {
+    struct cell *cell;
+    struct cell_node *next;
+};
+
+struct callback_node {
+    callback_id id;
+    void *obj;
+    callback func;
+    struct callback_node *next;
+};
+
+struct reactor {
+    struct cell_node *cells;
+};
+
+enum cell_type { INPUT_CELL, COMPUTE1_CELL, COMPUTE2_CELL };
+
+struct cell{
+    int value;
+    int old_value;
+    enum cell_type type;
+
+    struct cell *parent1;
+    struct cell *parent2;
+
+    union {
+        compute1 fun1;
+        compute2 fun2;
+    } fun;
+
+    struct cell_node *dependents;
+    struct callback_node *callbacks;
+
+    bool changed;
+};
+
+struct reactor *create_reactor(void){
+    return calloc(1, sizeof(struct reactor));
+}
+
+void destroy_reactor(struct reactor *reactor) {
+    if (reactor) {
+        struct cell_node *node = reactor->cells;
+        while (node) {
+            struct callback_node *callback = node->cell->callbacks;
+            while (callback) {
+                struct callback_node *temp1 = callback->next;
+                free(callback);
+                callback = temp1;
+            }
+
+            struct cell_node *dependent = node->cell->dependents;
+            while (dependent) {
+                struct cell_node *temp1 = dependent->next;
+                free(dependent);
+                dependent = temp1;
+            }
+
+            struct cell_node *temp = node->next;
+
+            free(node->cell);
+            free(node);
+            node = temp;
+        }
+        free(reactor);
+    }
+}
+
+struct cell *create_input_cell(struct reactor *reactor, int initial_value){
+    if (!reactor) return NULL;
+
+    struct cell_node *new_node = malloc(sizeof(struct cell_node));
+    if (!new_node) return NULL;
+
+    struct cell *new_cell = calloc(1, sizeof(struct cell));
+    if (!new_cell) return NULL;
+
+    new_cell->type = INPUT_CELL;
+    new_cell->value = initial_value;
+
+    new_node->cell = new_cell;
+    new_node->next = reactor->cells;
+    reactor->cells = new_node;
+
+    return new_cell;
+}
+
+struct cell *create_compute1_cell(struct reactor *reactor, struct cell *parent, compute1 fun){
+    if (!reactor) return NULL;
+
+    struct cell_node *new_node = malloc(sizeof(struct cell_node));
+    if (!new_node) return NULL;
+
+    struct cell_node *new_dependent = malloc(sizeof(struct cell_node));
+    if (!new_dependent) return NULL;
+
+    struct cell *new_cell = calloc(1, sizeof(struct cell));
+    if (!new_cell) return NULL;
+
+    new_cell->type = COMPUTE1_CELL;
+    new_cell->fun.fun1 = fun;
+    new_cell->parent1 = parent;
+
+    new_cell->value = fun(parent->value);
+
+    new_dependent->cell = new_cell;
+    new_dependent->next = parent->dependents;
+    parent->dependents = new_dependent;
+
+    new_node->cell = new_cell;
+    new_node->next = reactor->cells;
+    reactor->cells = new_node;
+
+    return new_cell;
+}
+
+struct cell *create_compute2_cell(struct reactor *reactor, struct cell *parent1,
+                                  struct cell *parent2, compute2 fun){
+    if (!reactor) return NULL;
+
+    struct cell_node *new_node = malloc(sizeof(struct cell_node));
+    if (!new_node) return NULL;
+
+    struct cell_node *new_dependent_node1 = malloc(sizeof(struct cell_node));
+    if (!new_dependent_node1) return NULL;
+
+    struct cell_node *new_dependent_node2 = malloc(sizeof(struct cell_node));
+    if (!new_dependent_node2) return NULL;
+
+    struct cell *new_cell = calloc(1, sizeof(struct cell));
+    if (!new_cell) return NULL;
+
+    new_cell->type = COMPUTE2_CELL;
+    new_cell->fun.fun2 = fun;
+    new_cell->parent1 = parent1;
+    new_cell->parent2 = parent2;
+
+    new_cell->value = fun(parent1->value, parent2->value);
+
+    new_dependent_node1->cell = new_cell;
+    new_dependent_node2->cell = new_cell;
+
+    new_dependent_node1->next = parent1->dependents;
+    parent1->dependents = new_dependent_node1;
+
+    new_dependent_node2->next = parent2->dependents;
+    parent2->dependents = new_dependent_node2;
+
+    new_node->cell = new_cell;
+    new_node->next = reactor->cells;
+    reactor->cells = new_node;
+
+    return new_cell;
+}
+
+static inline bool update_value(struct cell *cell){
+    if (cell->type == INPUT_CELL) return false;
+
+    int new_value;
+    if (cell->type == COMPUTE1_CELL) {
+        new_value = cell->fun.fun1(cell->parent1->value);
+    } else {
+        new_value = cell->fun.fun2(cell->parent1->value, cell->parent2->value);
+    }
+
+    if (cell->value == new_value) return false;
+
+    cell->value = new_value;
+
+    return true;
+}
+
+int get_cell_value(struct cell *cell){
+    return cell->value;
+}
+
+static void push_dependents(struct cell_node **work, struct cell_node *dependents){
+    while (dependents) {
+        struct cell_node *node = malloc(sizeof(struct cell_node));
+        node->cell = dependents->cell;
+        node->next = *work;
+        *work = node;
+        dependents = dependents->next;
+    }
+}
+
+void set_cell_value(struct cell *cell, int new_value){
+    if (cell->type != INPUT_CELL || cell->value == new_value) {
+        return;
+    }
+
+    cell->value = new_value;
+
+    struct cell_node *work_list = NULL;
+    struct cell_node *changed_cells = NULL;
+
+    push_dependents(&work_list, cell->dependents);
+
+    while (work_list) {
+        struct cell_node *current_node = work_list;
+        struct cell *current_cell = current_node->cell;
+
+        work_list = current_node->next;
+        free(current_node);
+
+        int previous_value = current_cell->value;
+
+        if (update_value(current_cell)) {
+
+            if (!current_cell->changed) {
+                current_cell->changed = true;
+
+                current_cell->old_value = previous_value;
+
+                struct cell_node *changed_node = malloc(sizeof(struct cell_node));
+                changed_node->cell = current_cell;
+                changed_node->next = changed_cells;
+                changed_cells = changed_node;
+            }
+
+            push_dependents(&work_list, current_cell->dependents);
+        }
+    }
+
+    while (changed_cells) {
+        struct cell_node *current_node = changed_cells;
+        struct cell *current_cell = current_node->cell;
+
+        if (current_cell->value != current_cell->old_value) {
+            struct callback_node *callback = current_cell->callbacks;
+            while (callback) {
+                callback->func(callback->obj, current_cell->value);
+                callback = callback->next;
+            }
+        }
+
+        current_cell->changed = false;
+        changed_cells = current_node->next;
+        free(current_node);
+    }
+}
+
+// The callback should be called with the same void * given in add_callback.
+callback_id add_callback(struct cell *cell, void *obj, callback callback){
+    static callback_id id = 0;
+
+    struct callback_node *new_node = calloc(1, sizeof(struct callback_node));
+    assert(new_node);
+
+    new_node->func = callback;
+    new_node->obj = obj;
+
+    new_node->next = cell->callbacks;
+    cell->callbacks = new_node;
+    new_node->id = id;
+
+    id++;
+    return new_node->id;
+}
+
+void remove_callback(struct cell *cell, callback_id id){
+    struct callback_node *callback = cell->callbacks;
+    if (!callback) return;
+
+    if (callback->id == id) {
+        cell->callbacks = callback->next;
+        free(callback);
+        return;
+    }
+
+    struct callback_node *next_callback = callback->next;
+
+    while (next_callback) {
+        if (next_callback->id == id) {
+            callback->next = next_callback->next;
+            free(next_callback);
+            return;
+        }
+
+        callback = next_callback;
+        next_callback = next_callback->next;
+    }
+}
diff --git a/solutions/c/react/1/react.h b/solutions/c/react/1/react.h
new file mode 100644
index 0000000..9a0ff89
--- /dev/null
+++ b/solutions/c/react/1/react.h
@@ -0,0 +1,29 @@
+#ifndef REACT_H
+#define REACT_H
+
+struct reactor;
+struct cell;
+
+typedef int (*compute1)(int);
+typedef int (*compute2)(int, int);
+
+struct reactor *create_reactor(void);
+// destroy_reactor should free all cells created under that reactor.
+void destroy_reactor(struct reactor *);
+
+struct cell *create_input_cell(struct reactor *, int initial_value);
+struct cell *create_compute1_cell(struct reactor *, struct cell *, compute1);
+struct cell *create_compute2_cell(struct reactor *, struct cell *,
+                                  struct cell *, compute2);
+
+int get_cell_value(struct cell *);
+void set_cell_value(struct cell *, int new_value);
+
+typedef void (*callback)(void *, int);
+typedef int callback_id;
+
+// The callback should be called with the same void * given in add_callback.
+callback_id add_callback(struct cell *, void *, callback);
+void remove_callback(struct cell *, callback_id);
+
+#endif