二叉树的三种遍历方式（递归）
先根
1void preOrder(BinTree tree){
2 if(tree == NULL){
3 return ;
4 }
5 visit(tree);
6 preOrder(tree->leftNode);
7 preOrder(tree->rightNode);
8}
中根
1void inOrder(BinTree tree){
2 if(tree == NULL){
3 return ;
4 }
5 inOrder(tree->leftNode);
6 visit(tree);
7 inOrder(tree->rightNode);
8}
后根
1void postOrder(BinTree tree){
2 if(tree == NULL){
3 return ;
4 }
5 postOrder(tree->leftNode);
6 postOrder(tree->rightNode);
7 visit(tree);
8}