diff --git a/103_binary_tree_zigzag_level_order_traversal/Makefile b/103_binary_tree_zigzag_level_order_traversal/Makefile
new file mode 100644
index 0000000..48851f2
--- /dev/null
+++ b/103_binary_tree_zigzag_level_order_traversal/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test bst_zigzag.c
diff --git a/103_binary_tree_zigzag_level_order_traversal/bst_zigzag.c b/103_binary_tree_zigzag_level_order_traversal/bst_zigzag.c
new file mode 100644
index 0000000..fae68dc
--- /dev/null
+++ b/103_binary_tree_zigzag_level_order_traversal/bst_zigzag.c
@@ -0,0 +1,235 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define BST_MAX_LEVEL 800
+
+#define container_of(ptr, type, member) \
+    ((type *)((char *)(ptr) - (size_t)&(((type *)0)->member)))
+
+#define list_entry(ptr, type, member) \
+    container_of(ptr, type, member)
+
+#define	list_first_entry(ptr, type, field)  list_entry((ptr)->next, type, field)
+#define	list_last_entry(ptr, type, field)  list_entry((ptr)->prev, type, field)
+
+#define	list_for_each(p, head) \
+	for (p = (head)->next; p != (head); p = p->next)
+
+#define	list_for_each_reverse(p, head) \
+	for (p = (head)->prev; p != (head); p = p->prev)
+
+#define	list_for_each_safe(p, n, head) \
+	for (p = (head)->next, n = p->next; p != (head); p = n, n = p->next)
+
+#define	list_for_each_safe_reverse(p, n, head) \
+	for (p = (head)->prev, n = p->prev; p != (head); p = n, n = p->prev)
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+struct list_head {
+    struct list_head *next, *prev;
+};
+
+static inline void INIT_LIST_HEAD(struct list_head *list)
+{
+    list->next = list->prev = list;
+}
+
+static inline int list_empty(const struct list_head *head)
+{
+    return head->next == head;
+}
+
+static inline void __list_add(struct list_head *new, struct list_head *prev, struct list_head *next)
+{
+    next->prev = new;
+    new->next = next;
+    new->prev = prev;
+    prev->next = new;
+}
+
+static inline void list_add(struct list_head *_new, struct list_head *head)
+{
+    __list_add(_new, head, head->next);
+}
+
+static inline void list_add_tail(struct list_head *_new, struct list_head *head)
+{
+    __list_add(_new, head->prev, head);
+}
+
+static inline void __list_del(struct list_head *entry)
+{
+    entry->next->prev = entry->prev;
+    entry->prev->next = entry->next;
+}
+
+static inline void list_del(struct list_head *entry)
+{
+    __list_del(entry);
+    entry->next = entry->prev = NULL;
+}
+
+struct bfs_node {
+    struct TreeNode *node;
+    struct list_head link;
+};
+
+static struct bfs_node *node_new(struct list_head *free_list, struct TreeNode *node)
+{
+    struct bfs_node *new;
+    if (list_empty(free_list)) {
+        new = malloc(sizeof(*new));
+    } else {
+        new = list_first_entry(free_list, struct bfs_node, link);
+        list_del(&new->link);
+    }
+    new->node = node;
+    return new;
+}
+
+static void queue(struct list_head *parents, struct list_head *children, int reverse,
+                  struct list_head *free_list, int **results, int *col_sizes, int level)
+{
+    struct list_head *p, *n;
+    struct bfs_node *new, *parent;
+
+    list_for_each(p, parents) {
+        parent = list_entry(p, struct bfs_node, link);
+        if (parent->node->left != NULL) {
+            new = node_new(free_list, parent->node->left);
+            list_add_tail(&new->link, children);
+        }
+        if (parent->node->right != NULL) {
+            new = node_new(free_list, parent->node->right);
+            list_add_tail(&new->link, children);
+        }
+        col_sizes[level]++;
+    }
+
+    int i = 0;
+    results[level] = malloc(col_sizes[level] * sizeof(int));
+    if (reverse) {
+        list_for_each_safe_reverse(p, n, parents) {
+            parent = list_entry(p, struct bfs_node, link);
+            results[level][i++] = parent->node->val;
+            list_del(p);
+            list_add(p, free_list);
+        }
+    } else {
+        list_for_each_safe(p, n, parents) {
+            parent = list_entry(p, struct bfs_node, link);
+            results[level][i++] = parent->node->val;
+            list_del(p);
+            list_add(p, free_list);
+        }
+    }
+}
+
+/**
+ ** Return an array of arrays of size *returnSize.
+ ** The sizes of the arrays are returned as *columnSizes array.
+ ** Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
+ **/
+static int** zigzagLevelOrder(struct TreeNode* root, int** columnSizes, int* returnSize)
+{
+    if (root == NULL) {
+        *returnSize = 0;
+        return NULL;
+    }
+
+    struct list_head free_list;
+    struct list_head q0;
+    struct list_head q1;
+    INIT_LIST_HEAD(&free_list);
+    INIT_LIST_HEAD(&q0);
+    INIT_LIST_HEAD(&q1);
+
+    int **results = malloc(BST_MAX_LEVEL * sizeof(int *));
+    *columnSizes = malloc(BST_MAX_LEVEL * sizeof(int));
+    memset(*columnSizes, 0, BST_MAX_LEVEL * sizeof(int));
+
+    int level = 0;
+    struct bfs_node *new = node_new(&free_list, root);
+    list_add_tail(&new->link, &q0);
+
+    while (!list_empty(&q0) || !list_empty(&q1)) {
+        if (level & 0x1) {
+            queue(&q1, &q0, 1, &free_list, results, *columnSizes, level);
+        } else {
+            queue(&q0, &q1, 0, &free_list, results, *columnSizes, level);
+        }
+        level++;
+    }
+
+    *returnSize = level;
+    return results;
+}
+
+int main(void)
+{
+#if 1
+    struct TreeNode root;
+    root.val = 3;
+
+    struct TreeNode node1[2];
+    node1[0].val = 9;
+    node1[1].val = 20;
+
+    struct TreeNode node2[4];
+    node2[2].val = 15;
+    node2[3].val = 7;
+
+    root.left = &node1[0];
+    root.right = &node1[1];
+
+    node1[0].left = NULL;
+    node1[0].right = NULL;
+    node1[1].left = &node2[2];
+    node1[1].right = &node2[3];
+#else
+    struct TreeNode root;
+    root.val = 1;
+
+    struct TreeNode node1[2];
+    node1[0].val = 2;
+    node1[1].val = 3;
+
+    struct TreeNode node2[4];
+    node2[0].val = 4;
+    node2[3].val = 5;
+
+    root.left = &node1[0];
+    root.right = &node1[1];
+
+    node1[0].left = &node2[0];
+    node1[0].right = NULL;
+    node1[1].left = NULL;
+    node1[1].right = &node2[3];
+#endif
+
+    node2[0].left = NULL;
+    node2[0].right = NULL;
+    node2[1].left = NULL;
+    node2[1].right = NULL;
+    node2[2].left = NULL;
+    node2[2].right = NULL;
+    node2[3].left = NULL;
+    node2[3].right = NULL;
+
+    int i, j, count = 0, *col_sizes;
+    int **lists = zigzagLevelOrder(&root, &col_sizes, &count);
+    for (i = 0; i < count; i++) {
+        for (j = 0; j < col_sizes[i]; j++) {
+            printf("%d ", lists[i][j]);
+        }
+        printf("\n");
+    }
+
+    return 0;
+}
diff --git a/107_binary_tree_level_order_traversal_ii/Makefile b/107_binary_tree_level_order_traversal_ii/Makefile
new file mode 100644
index 0000000..d8026db
--- /dev/null
+++ b/107_binary_tree_level_order_traversal_ii/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test bst_bfs.c
diff --git a/107_binary_tree_level_order_traversal_ii/bst_bfs.c b/107_binary_tree_level_order_traversal_ii/bst_bfs.c
new file mode 100644
index 0000000..b9cc5ba
--- /dev/null
+++ b/107_binary_tree_level_order_traversal_ii/bst_bfs.c
@@ -0,0 +1,208 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define BST_MAX_LEVEL 800
+
+#define container_of(ptr, type, member) \
+    ((type *)((char *)(ptr) - (size_t)&(((type *)0)->member)))
+
+#define list_entry(ptr, type, member) \
+    container_of(ptr, type, member)
+
+#define	list_first_entry(ptr, type, field)  list_entry((ptr)->next, type, field)
+#define	list_last_entry(ptr, type, field)  list_entry((ptr)->prev, type, field)
+
+#define	list_for_each(p, head) \
+	for (p = (head)->next; p != (head); p = p->next)
+
+#define	list_for_each_safe(p, n, head) \
+	for (p = (head)->next, n = p->next; p != (head); p = n, n = p->next)
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+struct list_head {
+    struct list_head *next, *prev;
+};
+
+static inline void INIT_LIST_HEAD(struct list_head *list)
+{
+    list->next = list->prev = list;
+}
+
+static inline int list_empty(const struct list_head *head)
+{
+    return (head->next == head);
+}
+
+static inline void __list_add(struct list_head *new, struct list_head *prev, struct list_head *next)
+{
+    next->prev = new;
+    new->next = next;
+    new->prev = prev;
+    prev->next = new;
+}
+
+static inline void list_add(struct list_head *_new, struct list_head *head)
+{
+    __list_add(_new, head, head->next);
+}
+
+static inline void list_add_tail(struct list_head *_new, struct list_head *head)
+{
+    __list_add(_new, head->prev, head);
+}
+
+static inline void __list_del(struct list_head *entry)
+{
+    entry->next->prev = entry->prev;
+    entry->prev->next = entry->next;
+}
+
+static inline void list_del(struct list_head *entry)
+{
+    __list_del(entry);
+    entry->next = entry->prev = NULL;
+}
+
+struct bfs_node {
+    struct TreeNode *node;
+    struct list_head link;
+};
+
+static struct bfs_node *node_new(struct list_head *free_list, struct TreeNode *node)
+{
+    struct bfs_node *new;
+    if (list_empty(free_list)) {
+        new = malloc(sizeof(*new));
+    } else {
+        new = list_first_entry(free_list, struct bfs_node, link);
+        list_del(&new->link);
+    }
+    new->node = node;
+    return new;
+}
+
+static void queue(struct list_head *parents, struct list_head *children,
+                  struct list_head *free_list, int **results, int *col_sizes, int level)
+{
+    struct list_head *p, *n;
+    list_for_each(p, parents) {
+        struct bfs_node *new;
+        struct bfs_node *parent = list_entry(p, struct bfs_node, link);
+        if (parent->node->left != NULL) {
+            new = node_new(free_list, parent->node->left);
+            list_add_tail(&new->link, children);
+        }
+        if (parent->node->right != NULL) {
+            new = node_new(free_list, parent->node->right);
+            list_add_tail(&new->link, children);
+        }
+        col_sizes[level]++;
+    }
+
+    int i = 0;
+    results[level] = malloc(col_sizes[level] * sizeof(int));
+    list_for_each_safe(p, n, parents) {
+        struct bfs_node *parent = list_entry(p, struct bfs_node, link);
+        results[level][i++] = parent->node->val;
+        list_del(p);
+        list_add(p, free_list);
+    }
+}
+
+/**
+ ** Return an array of arrays of size *returnSize.
+ ** The sizes of the arrays are returned as *columnSizes array.
+ ** Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
+ **/
+static int** levelOrderBottom(struct TreeNode* root, int** columnSizes, int* returnSize)
+{
+    if (root == NULL) {
+        *returnSize = 0;
+        return NULL;
+    }
+
+    struct list_head free_list;
+    struct list_head q0;
+    struct list_head q1;
+    INIT_LIST_HEAD(&free_list);
+    INIT_LIST_HEAD(&q0);
+    INIT_LIST_HEAD(&q1);
+
+    int **results = malloc(BST_MAX_LEVEL * sizeof(int *));
+    *columnSizes = malloc(BST_MAX_LEVEL * sizeof(int));
+    memset(*columnSizes, 0, BST_MAX_LEVEL * sizeof(int));
+
+    int level = 0;
+    struct bfs_node *new = node_new(&free_list, root);
+    list_add_tail(&new->link, &q0);
+
+    while (!list_empty(&q0) || !list_empty(&q1)) {
+        if (level & 0x1) {
+            queue(&q1, &q0, &free_list, results, *columnSizes, level);
+        } else {
+            queue(&q0, &q1, &free_list, results, *columnSizes, level);
+        }
+        level++;
+    }
+
+    *returnSize = level;
+
+    int i, j;
+    for (i = 0, j = level - 1; i < j; i++, j--) {
+        int *tmp = results[i];
+        results[i] = results[j];
+        results[j] = tmp;
+        int t = (*columnSizes)[i];
+        (*columnSizes)[i] = (*columnSizes)[j];
+        (*columnSizes)[j] = t;
+    }
+    return results;
+}
+
+int main(void)
+{
+    struct TreeNode root;
+    root.val = 3;
+
+    struct TreeNode node1[2];
+    node1[0].val = 9;
+    node1[1].val = 20;
+
+    struct TreeNode node2[4];
+    node2[2].val = 15;
+    node2[3].val = 7;
+
+    root.left = &node1[0];
+    root.right = &node1[1];
+
+    node1[0].left = NULL;
+    node1[0].right = NULL;
+    node1[1].left = &node2[2];
+    node1[1].right = &node2[3];
+
+    node2[0].left = NULL;
+    node2[0].right = NULL;
+    node2[1].left = NULL;
+    node2[1].right = NULL;
+    node2[2].left = NULL;
+    node2[2].right = NULL;
+    node2[3].left = NULL;
+    node2[3].right = NULL;
+
+    int i, j, count = 0, *col_sizes;
+    int **lists = levelOrderBottom(&root, &col_sizes, &count);
+    for (i = 0; i < count; i++) {
+        for (j = 0; j < col_sizes[i]; j++) {
+            printf("%d ", lists[i][j]);
+        }
+        printf("\n");
+    }
+
+    return 0;
+}