遍历二叉树(递归法)

前序遍历

/_src/c/binary-tree/traverse/traverse.c
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/**
 * preorder traverse a binary tree
 **/
void
preorder_traverse(struct binary_tree_node *root,
    void handle(struct binary_tree_node *))
{
    // return immediately if given tree is NULL
    if (root == NULL) {
        return;
    }

    // handle root node before traversing subtrees
    handle(root);

    // traverse left subtree recursively if not NULL
    if (root->left) {
        preorder_traverse(root->left, handle);
    }

    // traverse right subtree recursively if not NULL
    if (root->right) {
        preorder_traverse(root->right, handle);
    }
}

中序遍历

/_src/c/binary-tree/traverse/traverse.c
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/**
 * inorder traverse a binary tree
 **/
void
inorder_traverse(struct binary_tree_node *root,
    void handle(struct binary_tree_node *))
{
    // return immediately if given tree is NULL
    if (root == NULL) {
        return;
    }

    // traverse left subtree recursively if not NULL
    if (root->left) {
        inorder_traverse(root->left, handle);
    }

    // handle root node
    handle(root);

    // traverse right subtree recursively if not NULL
    if (root->right) {
        inorder_traverse(root->right, handle);
    }
}

后序遍历

/_src/c/binary-tree/traverse/traverse.c
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/**
 * postorder traverse a binary tree
 **/
void
postorder_traverse(struct binary_tree_node *root,
    void handle(struct binary_tree_node *))
{
    // return immediately if given tree is NULL
    if (root == NULL) {
        return;
    }

    // traverse left subtree recursively if not NULL
    if (root->left) {
        postorder_traverse(root->left, handle);
    }

    // traverse right subtree recursively if not NULL
    if (root->right) {
        postorder_traverse(root->right, handle);
    }

    // traverse right subtree recursively if not NULL
    handle(root);
}