Publish the C codes to the docs. (#469)

docs/chapter_tree/binary_tree.md

@@ -87,7 +87,27 @@
 === "C"
 
     ```c title=""
-    
+    /* 二叉树节点结构体 */
+    struct TreeNode {
+        int val;                // 节点值
+        int height;             // 节点高度
+        struct TreeNode *left;  // 左子节点指针
+        struct TreeNode *right; // 右子节点指针
+    };
+
+    typedef struct TreeNode TreeNode;
+
+    /* 构造函数 */
+    TreeNode *newTreeNode(int val) {
+        TreeNode *node;
+
+        node = (TreeNode *)malloc(sizeof(TreeNode));
+        node->val = val;
+        node->height = 0;
+        node->left = NULL;
+        node->right = NULL;
+        return node;
+    }
     ```
 
 === "C#"
@@ -256,7 +276,18 @@
 === "C"
 
     ```c title="binary_tree.c"
-    
+    /* 初始化二叉树 */
+    // 初始化节点
+    TreeNode *n1 = newTreeNode(1);
+    TreeNode *n2 = newTreeNode(2);
+    TreeNode *n3 = newTreeNode(3);
+    TreeNode *n4 = newTreeNode(4);
+    TreeNode *n5 = newTreeNode(5);
+    // 构建引用指向（即指针）
+    n1->left = n2;
+    n1->right = n3;
+    n2->left = n4;
+    n2->right = n5;
     ```
 
 === "C#"
@@ -376,7 +407,13 @@
 === "C"
 
     ```c title="binary_tree.c"
-    
+    /* 插入与删除节点 */
+    TreeNode *P = newTreeNode(0);
+    // 在 n1 -> n2 中间插入节点 P
+    n1->left = P;
+    P->left = n2;
+    // 删除节点 P
+    n1->left = n2;
     ```
 
 === "C#"