diff --git a/assignment1/problem3/Makefile b/assignment1/problem3/Makefile
new file mode 100644
index 0000000..a96763e
--- /dev/null
+++ b/assignment1/problem3/Makefile
@@ -0,0 +1,5 @@
+EXEC = uncompress
+SRC = $(wildcard *.c)
+
+$(EXEC): $(SRC)
+	gcc -o $@ $^ -Wall
diff --git a/assignment1/problem3/stack.c b/assignment1/problem3/stack.c
new file mode 100644
index 0000000..aa94f90
--- /dev/null
+++ b/assignment1/problem3/stack.c
@@ -0,0 +1,123 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_Problem_3
+ * Stack, with functioin automaticlly increase the size
+ */
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <assert.h>
+
+#include "stack.h"
+
+
+bool CreateStack(Stack *stack, int size) {
+	/* check */
+	assert(size > 0);
+
+	/* memory allocate */
+	stack->data = (ASTNode **)malloc(sizeof(ASTNode *) * 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 - 1 */
+	return stack->top == stack->size - 1;
+}
+
+bool Top(Stack *stack, ASTNode **x) {
+	/* check empty */
+	if (IsEmpty(stack)) {
+		return false;
+	}
+
+	/* get top */
+	*x = stack->data[stack->top];
+
+	return true;
+}
+
+bool Push(Stack *stack, ASTNode *x) {
+	/* check, enlarge stack */
+	if (IsFull(stack)) {
+		Stack newStack;
+
+		/* create new stack, with 2 bigger size */
+		CreateStack(&newStack, stack->size * 2);
+
+		/* copy data */
+		memcpy(newStack.data, stack->data, stack->size * sizeof(ASTNode *));
+		newStack.top = stack->top;
+
+		/* delete old stack */
+		DestroyStack(stack);
+		
+		/* set new stack */
+		*stack = newStack;
+	}
+
+	/* push */
+	stack->data[++stack->top] = x;
+
+	return true;
+}
+
+bool Pop(Stack *stack, ASTNode **x) {
+	/* check */
+	if (IsEmpty(stack)) {
+		return false;
+	}
+
+	/* get x, and top - 1 */
+	*x = stack->data[stack->top--];
+	return true;
+}
+
+void DisplayStack(Stack *stack) {
+	ASTNode **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("|  %p  |\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/problem3/stack.h b/assignment1/problem3/stack.h
new file mode 100644
index 0000000..e51cfd6
--- /dev/null
+++ b/assignment1/problem3/stack.h
@@ -0,0 +1,41 @@
+#ifndef MY_STACK_H
+#define MY_STACK_H
+
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_Problem_3
+ * Stack, with functioin automaticlly increase the size
+ */
+
+#include <stdbool.h>
+
+#include "struct.h"
+
+#define DEFAULT_STACK_SIZE 16
+
+/* create an stack, size will automaticlly increase */
+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, ASTNode **x);
+
+/* add a value to stack */
+bool Push(Stack *stack, ASTNode *x);
+
+/* delete a value from stack */
+bool Pop(Stack *stack, ASTNode **x);
+
+/* print the stack */
+void DisplayStack(Stack *stack);
+
+/* delete a stack */
+void DestroyStack(Stack *stack);
+
+#endif
diff --git a/assignment1/problem3/struct.h b/assignment1/problem3/struct.h
new file mode 100644
index 0000000..b3e7908
--- /dev/null
+++ b/assignment1/problem3/struct.h
@@ -0,0 +1,74 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_Problem_3
+ * the shared data structure
+ */
+
+#ifndef MY_STRUCT_H
+#define MY_STRUCT_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+
+/* Used for AST Node's string */
+typedef struct ASTString_str {
+	char *string;
+
+	/* the start index */
+	size_t start;
+
+	/* the end index */
+	size_t end;
+
+} ASTString;
+
+/* AST Node structure, describe in ./README.md */
+typedef struct ASTNode_str {
+
+	/* 1: string, 2: left (, 3: right ) */
+	char type;
+
+	/* valid when type==2 */
+	unsigned int repeat;
+
+	/* valid when type==1 */
+	ASTString string;
+
+	/* next node */
+	struct ASTNode_str *next;
+
+	/* child node */
+	struct ASTNode_str *child;
+} ASTNode;
+
+/* struct for stack */
+typedef struct Stack_str {
+	/* the size of stack */
+	int size;
+	/* top index, empty is -1 */
+	int top;
+	/* data */
+	ASTNode **data;
+} Stack;
+
+/* AST Scanner struct */
+typedef struct ASTScanner_str {
+	/* pointer to string, string will not be modified */
+	char *string;
+
+	size_t length;
+	size_t current_index;
+} ASTScanner;
+
+/* AST Tree structure */
+typedef struct ASTTree_str {
+	ASTNode *root;
+	ASTNode *currNode;
+	Stack stack;
+	size_t max;
+	size_t count;
+} ASTTree;
+
+#endif
diff --git a/assignment1/problem3/test_main.c b/assignment1/problem3/test_main.c
new file mode 100644
index 0000000..0bc78f5
--- /dev/null
+++ b/assignment1/problem3/test_main.c
@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "uncompress.h"
+
+int main() {
+	Uncompress(NULL, stdout);
+	Uncompress("", stdout);
+	Uncompress("abc", stdout);
+	Uncompress("a1(b)c", stdout);
+	Uncompress("a11(c)d", stdout);
+	Uncompress("3(a)2(bc)", stdout);
+	Uncompress("3(a2(c))", stdout);
+	Uncompress("2(abb3(cd))ef", stdout);
+	return 0;
+}
diff --git a/assignment1/problem3/uncompress.c b/assignment1/problem3/uncompress.c
new file mode 100644
index 0000000..d92ff0e
--- /dev/null
+++ b/assignment1/problem3/uncompress.c
@@ -0,0 +1,329 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "uncompress.h"
+#include "stack.h"
+
+ASTScanner *CreateASTScanner(char *string) {
+	/* Special case define in pdf */
+	if (string == NULL) {
+		string = "NULL";
+	}
+
+	/* allocate scanner memory space */
+	ASTScanner *scanner = (ASTScanner *)malloc(sizeof(ASTScanner));
+	if (scanner == NULL) {
+		fprintf(stderr, "allocate scanner memory failed\n");
+		exit(1);
+	}
+
+	/* init values */
+	scanner->string = string;
+	scanner->length = strlen(string);
+	scanner->current_index = 0;
+
+	return scanner;
+}
+
+char ASTScan(ASTScanner *scanner, ASTNode **ret_node) {
+	size_t i;
+
+	/* return if it reached the end */
+	if (scanner->current_index == scanner->length) {
+		*ret_node = NULL;
+		return 0;
+	}
+
+	/* allocate memory space */
+	ASTNode *node = (ASTNode *)calloc(1, sizeof(ASTNode));
+	if (node == NULL) {
+		fprintf(stderr, "allocate ASTNode memory failed\n");
+		exit(1);
+	}
+	
+	/* read until end or '(' or ')',
+	 * after the loop, i point after '(' or ')' */
+	i = scanner->current_index;
+	while (i < scanner->length) {
+		if (scanner->string[i]=='(' || scanner->string[i] == ')') {
+			i++;
+			break;
+		}
+		i++;
+	}
+
+	/* if read ( */
+	if (scanner->string[i-1] == '(') {
+		node->type = 2;
+
+		/* check is there is any number before ( */
+		if (i-1 == 0) {
+			fprintf(stderr, "Syntax error: invailed value of repeat at begining\n");
+			return 1;
+		}
+		if (!IsNumber(scanner->string[i-2])) {
+			fprintf(stderr, "Syntax error: invailed value of repeat at index %ld\n", i-1);
+			return 1;
+		}
+
+		/* get number and the string before the number */
+		node->repeat = GetNumber(scanner->string, scanner->current_index, i-1, &node->string);
+		/* if the string exists */
+		if (node->string.string) {
+			/* change type to 1 */
+			node->type = 1;
+			node->repeat = 0;
+			i = node->string.end;
+		}
+
+	/* if read ) */
+	} else if (scanner->string[i-1] == ')') {
+		node->type = 3;
+
+		/* if there are string before ) */
+		if (i-1 != scanner->current_index) {
+
+			/* change type to 1 */
+			node->type = 1;
+			node->string.string = scanner->string;
+			node->string.start = scanner->current_index;
+			node->string.end = i-1;
+			i = i - 1;
+		}
+
+	/* until the end is a string */
+	} else {
+		node->type = 1;
+		node->string.string = scanner->string;
+		node->string.start = scanner->current_index;
+		node->string.end = i;
+	}
+
+	/* set current_index */
+	scanner->current_index = i;
+
+	/* set return node */
+	*ret_node = node;
+
+	return 0;
+}
+
+unsigned int GetNumber(char *string, size_t start, size_t end, ASTString *other_string) {
+	unsigned int result = 0;
+	size_t index = end - 1;
+
+	/* convert string to integer */
+	for (unsigned count = 1; IsNumber(string[index]); index--, count++) {
+		result = result + (string[index] - '0') * Power(10, count);
+	}
+
+	/* if there is a string before the number,
+	 * set to other_string */
+	if (index + 1 != start) {
+		other_string->string = string;
+		other_string->start = start;
+		other_string->end = index + 1;
+	}
+
+	return result;
+}
+
+bool IsNumber(const char c) {
+	return c >= '0' && c <= '9';
+}
+
+unsigned int Power(int x, int y) {
+	unsigned int result = 1;
+	for (int i=1; i<y; i++) {
+		result = result * x;
+	}
+	return result;
+}
+
+void DEBUG_NODE(ASTNode *root) {
+	ASTNode *currNode = root;
+	while (currNode) {
+		printf("[%p] type: %d, next: %p, child: %p, repeat: %d, string: %ld-%ld\n",
+					currNode,
+					currNode->type,
+					currNode->next,
+					currNode->child,
+					currNode->repeat,
+					currNode->string.start,
+					currNode->string.end);
+
+		if (currNode->type == 2) {
+			/* recursion to child */
+			DEBUG_NODE(currNode->child);
+		}
+
+		/* move forward */
+		currNode = currNode->next;
+	}
+}
+
+void DestroyASTTree(ASTTree *tree) {
+	ASTNode *currNode, *delNode;
+
+	/* push root node into stack */
+	Push(&tree->stack, tree->root);
+
+	/* loop to destroy all node */
+	while (!IsEmpty(&tree->stack)) {
+
+		/* get node from stack */
+		Pop(&tree->stack, &currNode);
+
+		while (currNode) {
+
+			if (currNode->type == 2) {
+				/* store child node into stack */
+				Push(&tree->stack, currNode->child);
+			}
+
+			/* delete node */
+			delNode = currNode;
+			currNode = currNode->next;
+			free(delNode);
+		}
+	}
+
+	/* finally do not forget to free everything */
+	DestroyStack(&tree->stack);
+	free(tree);
+}
+
+ASTTree *CreateASTTree() {
+	/* allocate memory */
+	ASTTree *tree = (ASTTree *)calloc(1, sizeof(ASTTree));
+	if (tree == NULL) {
+		fprintf(stderr, "Can not allocate AST Tree memory\n");
+		exit(1);
+	}
+
+	/* create stack with tree */
+	CreateStack(&tree->stack, DEFAULT_STACK_SIZE);
+
+	return tree;
+}
+
+void ASTCompileTree(ASTTree *tree, FILE *file) {
+
+	ASTCompileNode(tree->root, file);
+
+	/* new line at the end */
+	fputc('\n', file);
+}
+
+void ASTCompileNode(ASTNode *root, FILE *file) {
+	ASTNode *currNode = root;
+
+	/* loop for node and its all next node */
+	for (; currNode; currNode = currNode->next) {
+
+		if (currNode->type == 2) {
+			/* repeat to compile child node */
+			for (int i=0; i<currNode->repeat; i++) {
+				/* recursion */
+				ASTCompileNode(currNode->child, file);
+			}
+
+		} else if (currNode->type == 1) {
+			/* print string */
+			for (size_t i=currNode->string.start; i<currNode->string.end; i++) {
+				fputc(currNode->string.string[i], file);
+			}
+		}
+	}
+}
+
+char ASTScanAll(ASTTree *tree, ASTScanner *scanner) {
+	bool goback = false;
+	char err;
+	ASTNode *node = NULL, *last = NULL;
+
+	/* scan the first (root) node */
+	ASTScan(scanner, &node);
+	tree->root = node;
+	tree->max++;
+	last = tree->root;
+
+	/* set last node as last type 2 node */
+	if (node != NULL) {
+		if (node->type == 2) {
+			Push(&tree->stack, node);
+		}
+	}
+
+	/* scan until end */
+	while(err = ASTScan(scanner, &node), node) {
+
+		/* raise error */
+		if (err != 0) {
+			return err;
+		}
+
+		/* set goback flag, set last node as last type 2 node */
+		if (node->type == 3) {
+			goback = true;
+			Pop(&tree->stack, &last);
+			free(node);
+			continue;
+		/* uf node type is 2, record in stack */
+		} else if (node->type == 2) {
+			Push(&tree->stack, node);
+		}
+
+		/* connect to last node */
+		if (last->type == 1) {
+			last->next = node;
+		} else if (last->type == 2) {
+			if (goback) {
+				last->next = node;
+				goback = false;
+			} else {
+				last->child = node;
+			}
+		}
+
+		/* record last node, increase max */
+		last = node;
+		tree->max++;
+	}
+	return 0;
+}
+
+void Uncompress(char *string, FILE *file) {
+	char err;
+
+	/* create scanner and AST tree */
+	ASTScanner *scanner = CreateASTScanner(string);
+	ASTTree *tree = CreateASTTree();
+
+	/* scan all token into tree */
+	err = ASTScanAll(tree, scanner);
+	if (err != 0) {
+		fprintf(stderr, "EXITED");
+		exit(1);
+	}
+
+	/*
+	printf("---debug---\n");
+	DEBUG_NODE(tree->root);
+	printf("---debug---\n");
+	*/
+
+	/* compile */
+	ASTCompileTree(tree, file);
+
+	/* free memory */
+	DestroyASTTree(tree);
+	DestroyASTScanner(scanner);
+}
+
+void DestroyASTScanner(ASTScanner *scanner) {
+	free(scanner);
+}
diff --git a/assignment1/problem3/uncompress.h b/assignment1/problem3/uncompress.h
new file mode 100644
index 0000000..dcec38b
--- /dev/null
+++ b/assignment1/problem3/uncompress.h
@@ -0,0 +1,49 @@
+#ifndef UNCOMPRESS
+#define UNCOMPRESS
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "struct.h"
+
+/* return a pointer of a new scanner, string will not be copied */
+ASTScanner *CreateASTScanner(char *string);
+
+/* return a pointer of a new Tree */
+ASTTree *CreateASTTree();
+
+/* return a pointer of a token, return NULL if reached the end */
+char ASTScan(ASTScanner *scanner, ASTNode **ret_node);
+
+/* scan all token from scanner into tree */
+char ASTScanAll(ASTTree *tree, ASTScanner *scanner);
+
+/* return the number before a string with index */
+unsigned int GetNumber(char *string, size_t start, size_t end, ASTString *other_string);
+
+/* Useful function to check whether a char is a number */
+bool IsNumber(const char c);
+
+/* math calc, Power(10, 4) return 10000 */
+unsigned int Power(int x, int y);
+
+/* destroy AST scanner, memory of string will not be free */
+void DestroyASTScanner(ASTScanner *scanner);
+
+/* Destroy AST Tree */
+void DestroyASTTree(ASTTree *tree);
+
+/* Display debug information to screen from root node */
+void DEBUG_NODE(ASTNode *root);
+
+/* Compile the tree to file stream */
+void ASTCompileTree(ASTTree *tree, FILE *file);
+
+/* Compile node and its all next node to file stream */
+void ASTCompileNode(ASTNode *root, FILE *file);
+
+/* A short cut function, directly uncompress the raw string to file stream */
+void Uncompress(char *string, FILE *file);
+
+#endif