vector<int> postorderTraversal(TreeNode *root) {
vector<int> result;
TreeNode dummy(-1);
TreeNode *cur, *prev = nullptr;
std::function < void(const TreeNode*)> visit =
[&result](const TreeNode *node){
result.push_back(node->val);
};
dummy.left = root;
cur = &dummy;
while (cur != nullptr) {
if (cur->left == nullptr) {
prev = cur; /* 必须要有 */
cur = cur->right;
} else {
TreeNode *node = cur->left;
while (node->right != nullptr && node->right != cur)
node = node->right;
if (node->right == nullptr) { /* 还没线索化，则建立线索 */
node->right = cur;
prev = cur; /* 必须要有 */
cur = cur->left;
} else { /* 已经线索化，则访问节点，并删除线索 */
visit_reverse(cur->left, prev, visit);
prev->right = nullptr;
prev = cur; /* 必须要有 */
cur = cur->right;
}
}
}
return result;
}
// morris traversal
vector<int> postorderTraversal(TreeNode *root) {
vector<int> result;
TreeNode dummy(-1);
TreeNode *cur, *prev = nullptr;
std::function < void(const TreeNode*)> visit =
[&result](const TreeNode *node){
result.push_back(node->val);
};
dummy.left = root;
cur = &dummy;
while (cur != nullptr) {
if (cur->left == nullptr) {
prev = cur; //------------------------------- prev为cur的parent------------------------------------------------
cur = cur->right;
}
else {
TreeNode *node = cur->left;
while (node->right != nullptr && node->right != cur)
node = node->right;
if (node->right == nullptr) {
node->right = cur;
prev = cur;
cur = cur->left;
}
else {
visit_reverse(cur->left, prev, visit);
prev->right = nullptr;
prev = cur;
cur = cur->right;
}
}
}
return result;
}
