修改目录结构，优化CMakeLists

src/104.c

@@ -0,0 +1,19 @@
+#include "include/TreeNode.h"
+
+int max(const int a, const int b)
+{
+    return a > b ? a : b;
+}
+
+int maxDepth(struct TreeNode *root)
+{
+    if (!root)
+        return 0;
+
+    return max(maxDepth(root->left), maxDepth(root->right)) + 1;
+}
+
+int main()
+{
+    return 0;
+}