count nodes of binary tree (#56)

Author: realDuYuanChao

datastructures/binarytree/count_nodes_of_binary_tree.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+typedef int ElemType;
+typedef struct Node {
+    ElemType data;
+    struct Node *left;
+    struct Node *right;
+} Node;
+
+/**
+ * Create a new node with given data.
+ * @param data the data store at node.
+ * @return new node.
+ */
+Node *createNode(int data) {
+    Node *newNode = (malloc(sizeof(Node)));
+    newNode->data = data;
+    return newNode;
+}
+
+/**
+ * Return the count of nodes of binary tree.
+ * @param root the root node of binary tree.
+ * @return the count of nodes of binary tree.
+ */
+int countNodes(Node *root) {
+    return root == NULL ? 0 : 1 + countNodes(root->left) + countNodes(root->right);
+}
+
+void test() {
+    /* see images/example_binary_tree.png */
+    Node *root = createNode(1);
+    Node *node2 = createNode(2);
+    Node *node3 = createNode(3);
+    Node *node4 = createNode(4);
+    Node *node5 = createNode(5);
+
+    root->left = node2;
+    root->right = node3;
+
+    node2->left = node4;
+    node2->right = node5;
+
+    node3->left = node3->right = NULL;
+    node4->left = node4->right = NULL;
+    node5->left = node5->right = NULL;
+
+    assert(countNodes(root) == 5);
+}
+
+int main() {
+    test();
+    return 0;
+}