9

The Last Algorithms Course You'll Need/9. Stack.c

@@ -0,0 +1,103 @@
+#include <stdio.h>
+#include "stdlib.h"
+
+typedef int BOOL;
+#define TRUE 1
+#define FALSE 0
+
+typedef struct node 
+{
+	int value;
+	struct node *prev;
+} Node;
+
+typedef struct
+{
+	int value;
+	BOOL flag;
+} ListValue;
+
+static Node* HEAD;
+static Node* TAIL;
+
+static int LENGTH = 0;
+
+// O(1) operation, no growth by input
+BOOL push(int value)
+{
+	Node* new_head = malloc(sizeof(Node));
+	if (new_head == NULL)
+		return FALSE;
+
+	new_head->value = value;
+	new_head->prev = HEAD;
+
+	if (HEAD == NULL)
+		TAIL = new_head;
+
+	HEAD = new_head;
+	++LENGTH;
+
+	return TRUE;
+}
+
+// O(1) operation, no growth by input
+ListValue pop()
+{
+	ListValue value = { 0, FALSE };
+	Node* iterator = HEAD; 
+	if (iterator == NULL)
+		return value;
+
+	if (HEAD != TAIL)
+	{
+		HEAD = iterator->prev;
+	}
+	else
+	{
+		HEAD = NULL;
+		TAIL = NULL;
+	}
+
+	value.value = iterator->value;
+	value.flag = TRUE;
+
+	free(iterator);
+	iterator = NULL;
+
+	--LENGTH;
+	return value;
+}
+
+// O(1) operation, no growth by input
+ListValue peek()
+{
+	ListValue value = { 0, FALSE };
+	Node* iterator = HEAD; 
+	if (iterator == NULL)
+		return value;
+
+	value.value = iterator->value;
+	value.flag = TRUE;
+
+	return value;
+}
+
+int main()
+{
+	push(5);
+	push(22);
+	push(66);
+	push(122);
+	push(9);
+
+	printf("peek: %d\n", peek().value);
+
+	pop();
+
+	printf("peek: %d\n", peek().value);
+
+	pop();
+
+	printf("peek: %d\n", peek().value);
+}