diff --git a/assignment1/problem2/Makefile b/assignment1/problem2/Makefile
new file mode 100644
index 0000000..033fd88
--- /dev/null
+++ b/assignment1/problem2/Makefile
@@ -0,0 +1,5 @@
+EXEC = validbrackets
+SRC = $(wildcard *.c)
+
+$(EXEC): $(SRC)
+	gcc -o $@ $^ -Wall
diff --git a/assignment1/problem2/stack.c b/assignment1/problem2/stack.c
new file mode 100644
index 0000000..ea7126f
--- /dev/null
+++ b/assignment1/problem2/stack.c
@@ -0,0 +1,108 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_2
+ * stack lib, allow to create empty stack
+ */
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include <assert.h>
+
+#include "stack.h"
+
+bool CreateStack(Stack *stack, int size) {
+	/* check, allow create empty stack */
+	assert(size >= 0);
+
+	/* memory allocate */
+	stack->data = (char *)malloc(sizeof(char) * size);
+	if (stack->data == NULL) {
+		return false;
+	}
+
+	/* init attribute */
+	stack->top = -1;
+	stack->size = size;
+
+	return true;
+}
+
+bool IsEmpty(Stack *stack) {
+	/* if empty, stack->top = -1 */
+	return stack->top < 0;
+}
+
+bool IsFull(Stack *stack) {
+	/* if full, stack->top = stack->size */
+	return stack->top >= stack->size;
+}
+
+bool Top(Stack *stack, char *x) {
+	/* check empty */
+	if (IsEmpty(stack)) {
+		return false;
+	}
+
+	/* get top */
+	*x = stack->data[stack->top];
+
+	return true;
+}
+
+bool Push(Stack *stack, char x) {
+	/* check */
+	if (IsFull(stack)) {
+		return false;
+	}
+
+	/* push */
+	stack->data[++stack->top] = x;
+
+	return true;
+}
+
+bool Pop(Stack *stack, char *x) {
+	/* check */
+	if (IsEmpty(stack)) {
+		return false;
+	}
+
+	/* get x, and top - 1 */
+	*x = stack->data[stack->top--];
+	return true;
+}
+
+void DisplayStack(Stack *stack) {
+	char *top_p = stack->data + stack->top;
+
+	/* print the top pointer hint */
+	printf("top --> ");
+	
+	/* loop for stack data */
+	for (; top_p >= stack->data; top_p--) {
+
+		/* print top --> hint */
+		if (top_p != stack->data + stack->top) {
+			printf("        ");
+		}
+
+		printf("|  %c  |\n", *top_p);
+	}
+
+	/* print top --> hint */
+	if (top_p != stack->data + stack->top) {
+		printf("        ");
+	}
+
+	printf("+--------------+\n");
+}
+
+void DestroyStack(Stack *stack) {
+	free(stack->data);
+	stack->data = NULL;
+	stack->size = 0;
+	stack->top = -1;
+}
diff --git a/assignment1/problem2/stack.h b/assignment1/problem2/stack.h
new file mode 100644
index 0000000..2aa656b
--- /dev/null
+++ b/assignment1/problem2/stack.h
@@ -0,0 +1,47 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_2
+ * allow to create empty stack
+ */
+
+#ifndef MY_STACK
+#define MY_STACK
+
+#include <stdbool.h>
+
+/* struct for stack */
+typedef struct Stack_str {
+	/* the size of stack */
+	int size;
+	/* top index, empty is -1 */
+	int top;
+	/* data */
+	char *data;
+} Stack;
+
+/* create an stack with size */
+bool CreateStack(Stack *stack, int size);
+
+/* check a stack whether it contains data */
+bool IsEmpty(Stack *stack);
+
+/* check full of stack */
+bool IsFull(Stack *stack);
+
+/* get the top value of a stack */
+bool Top(Stack *stack, char *x);
+
+/* add a value to stack */
+bool Push(Stack *stack, char x);
+
+/* delete a value from stack */
+bool Pop(Stack *stack, char *x);
+
+/* print the stack */
+void DisplayStack(Stack *stack);
+
+/* delete a stack */
+void DestroyStack(Stack *stack);
+
+#endif
diff --git a/assignment1/problem2/test_main.c b/assignment1/problem2/test_main.c
new file mode 100644
index 0000000..57c44ee
--- /dev/null
+++ b/assignment1/problem2/test_main.c
@@ -0,0 +1,40 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_2
+ * Test function
+ */
+
+#include <stdio.h>
+#include <stddef.h>
+
+#include "validbrackets.h"
+
+/* test unit */
+typedef struct Unit_str {
+	char *text;
+	bool except;
+} Unit;
+
+int main() {
+
+	/* use for converting bool to string */
+	static char *BOOL_TEXT[] = {"false", "true"};
+
+	Unit *test;
+	static Unit case1 = {"{()<()>}[]", true};
+	static Unit case2 = {"(<)>", false};
+	static Unit case3 = {"{()}[", false};
+	static Unit case4 = {"", true};
+	static Unit case5 = {NULL, false};
+
+	static char *HINT = "Test '%s', except: %s, result: %s\n";
+
+	test = &case1; printf(HINT, test->text, BOOL_TEXT[test->except], BOOL_TEXT[ValidBrackets(test->text)]);
+	test = &case2; printf(HINT, test->text, BOOL_TEXT[test->except], BOOL_TEXT[ValidBrackets(test->text)]);
+	test = &case3; printf(HINT, test->text, BOOL_TEXT[test->except], BOOL_TEXT[ValidBrackets(test->text)]);
+	test = &case4; printf(HINT, test->text, BOOL_TEXT[test->except], BOOL_TEXT[ValidBrackets(test->text)]);
+	test = &case5; printf(HINT, test->text, BOOL_TEXT[test->except], BOOL_TEXT[ValidBrackets(test->text)]);
+
+	return 0;
+}
diff --git a/assignment1/problem2/validbrackets.c b/assignment1/problem2/validbrackets.c
new file mode 100644
index 0000000..e7b173a
--- /dev/null
+++ b/assignment1/problem2/validbrackets.c
@@ -0,0 +1,106 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_2
+ * validbrackets function
+ */
+
+#include <stddef.h>
+#include <string.h>
+
+#include "stack.h"
+#include "validbrackets.h"
+
+/* all the left brackets */
+static char LEFTBRACKETS[]  = "({[<";
+
+/* all the right brackets */
+static char RIGHTBRACKETS[] = ")}]>";
+
+/* number of brackets pairs */
+static int BRACKETS_LEN = 4;
+
+bool ValidBrackets(char *str) {
+
+	/* if string pass all the test, will return default value 'true' */
+	bool result = true;
+
+	/* null pointer will return false */
+	if (str == NULL) {
+		return false;
+	}
+	
+	/* tmp value to store the left brackets */
+	char left;
+	
+	/* length of string */
+	size_t str_len = strlen(str);
+
+	Stack stack;
+	/* only half length of the string is enougth,
+	 * empty stack is allowed */
+	CreateStack(&stack, str_len/2);
+
+	/* loop for all char in string */
+	for (size_t i=0; i<str_len; i++) {
+
+		/* full stack means the string is not vailed */
+		if (IsFull(&stack)) {
+			result = false;
+			break;
+		}
+
+		/* if it is not left brackets will return -1 */
+		if (IndexLeftBracket(str[i]) != -1) {
+			/* store the left brackets in stack */
+			Push(&stack, str[i]);
+		} else {
+			/* check empty stack before pop from stack */
+			if (IsEmpty(&stack)) {
+				result = false;
+				break;
+			}
+			/* get the pair left brackets from stack */
+			Pop(&stack, &left);
+
+			/* check if the left and right brackets matched */
+			if (!MatchBracket(left, str[i])) {
+				result = false;
+				break;
+			}
+		}
+	}
+	/* if finally the stack is not empty, return falsle */
+	if (!(IsEmpty(&stack))) {
+		result = false;
+	}
+	/* no memory leak */
+	DestroyStack(&stack);
+
+	return result;
+}
+
+int IndexLeftBracket(char c) {
+	for (int i=0; i<BRACKETS_LEN; i++) {
+		if (c == LEFTBRACKETS[i]) {
+			return i;
+		}
+	}
+	/* if c is not left brackets, return -1 */
+	return -1;
+}
+
+int IndexRightBracket(char c) {
+	for (int i=0; i<BRACKETS_LEN; i++) {
+		if (c == RIGHTBRACKETS[i]) {
+			return i;
+		}
+	}
+	/* if c is not right brackets, return -1 */
+	return -1;
+}
+
+bool MatchBracket(char left, char right) {
+	/* check whether left and right brackets are matched */
+	return IndexLeftBracket(left) == IndexRightBracket(right);
+}
diff --git a/assignment1/problem2/validbrackets.h b/assignment1/problem2/validbrackets.h
new file mode 100644
index 0000000..cf472e3
--- /dev/null
+++ b/assignment1/problem2/validbrackets.h
@@ -0,0 +1,31 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_2
+ * validbrackets header files
+ */
+
+#ifndef VAILDBRACKETS
+#define VAILDBRACKETS
+
+#include <stdbool.h>
+
+#include "stack.h"
+
+/* cvalid a string brackets,
+ * return true if empty string,
+ * return false if NULL string pointer */
+bool ValidBrackets(char *str);
+
+/* get the index number of left bracket,
+ * return -1 if c is not a left bracket */
+int IndexLeftBracket(char c);
+
+/* get the index number of right breacket,
+ * return -1 if c is not a left bracket */
+int IndexRightBracket(char c);
+
+/* compare two brackets if they match */
+bool MatchBracket(char left, char right);
+
+#endif