Binary search tree iterator

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>

Author: begeekmyfriend

173_binary_search_tree_iterator/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test bst_iter.c

173_binary_search_tree_iterator/bst_iter.c

@@ -0,0 +1,134 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+struct BSTIterator {
+    struct ListNode dummy;
+    struct ListNode *p;
+};
+
+static void bst_iter_generater(struct TreeNode *node, struct BSTIterator *iter)
+{
+    if (node->left != NULL) {
+        bst_iter_generater(node->left, iter);
+    }
+
+    struct ListNode *new = malloc(sizeof(*new));
+    new->val = node->val;
+    new->next = NULL;
+    if (iter->p != NULL) {
+        iter->p->next = new;
+    } else {
+        iter->dummy.next = new;
+    }
+    iter->p = new;
+
+    if (node->right != NULL) {
+        bst_iter_generater(node->right, iter);
+    }
+}
+
+static struct BSTIterator *bstIteratorCreate(struct TreeNode *root)
+{
+    struct BSTIterator *iter = malloc(sizeof(*iter));
+    if (root != NULL) {
+        iter->p = NULL;
+        bst_iter_generater(root, iter);
+    }
+    iter->p = &iter->dummy;
+    return iter;
+}
+
+/** @return whether we have a next smallest number */
+static bool bstIteratorHasNext(struct BSTIterator *iter)
+{
+    return iter->p->next != NULL;
+}
+
+/** @return the next smallest number */
+static int bstIteratorNext(struct BSTIterator *iter)
+{
+    iter->p = iter->p->next;
+    return iter->p->val;
+}
+
+/** Deallocates memory iteriously allocated for the iterator */
+static void bstIteratorFree(struct BSTIterator *iter)
+{
+    iter->p = iter->dummy.next;
+    while (iter->p != NULL) {
+        iter->dummy.next = iter->p->next;
+        free(iter->p);
+        iter->p = iter->dummy.next;
+    }
+}
+
+int main(void)
+{
+#if 1
+    struct TreeNode root;
+    root.val = 7;
+
+    struct TreeNode node1[2];
+    node1[0].val = 3;
+    node1[1].val = 15;
+
+    struct TreeNode node2[4];
+    node2[2].val = 9;
+    node2[3].val = 20;
+
+    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;
+
+    struct BSTIterator *i = bstIteratorCreate(&root);
+    while (bstIteratorHasNext(i)) {
+        printf("%d\n", bstIteratorNext(i));
+    }
+    bstIteratorFree(i);
+    return 0;
+}