From 365f1baabae9b2ccb3df1b4a4821bff58611f2de Mon Sep 17 00:00:00 2001
From: Kirill Petrashin <kirill8201@yandex.ru>
Date: Sat, 14 Mar 2026 12:13:01 +0300
Subject: implement a PositionStack

---
 stack.c | 23 +++++++++++++++++++++++
 stack.h | 18 +++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 stack.c

diff --git a/stack.c b/stack.c
new file mode 100644
index 0000000..bcdfbd3
--- /dev/null
+++ b/stack.c
@@ -0,0 +1,23 @@
+#include "stack.h"
+#include "structs.h"
+
+PositionStack ps_new(void) {
+    PositionStack ps;
+    ps.top = 0;
+    return ps;
+}
+
+int ps_push(PositionStack ps, Position pos) {
+    ps.arr[ps.top] = pos;
+    ps.top += 1;
+}
+
+Position ps_pop(PositionStack ps) {
+    ps.top -= 1;
+    return ps.arr[ps.top];
+}
+
+Position ps_peek(PositionStack ps) {
+    return ps.arr[ps.top - 1];
+}
+
diff --git a/stack.h b/stack.h
index 48fea92..a83a135 100644
--- a/stack.h
+++ b/stack.h
@@ -1,6 +1,22 @@
 #ifndef STACK_H_
 #define STACK_H_
 
-// TODO: implement a stack
+#include "structs.h"
+
+/* So, the implementation of the stack is array-based, for hyperspeed.
+ * For bigger maps we have to increase the STACK_SIZE, but it should
+ * work fine most of the time. I guess */
+#define STACK_SIZE 4096
+
+struct PositionStack_s {
+    Position arr[STACK_SIZE]; /* The array with all the values */
+    size_t top; /* Shows where the top of the stack is */
+};
+typedef struct PositionStack_s PositionStack;
+
+PositionStack ps_new(void); /* Returns an empty position stack */
+int ps_push(PositionStack ps, Position pos); /* Returns -1 if overflow */
+Position ps_pop(PositionStack ps);
+Position ps_peek(PositionStack ps);
 
 #endif /* STACK_H_ */
-- 
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