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Solution144.cpp

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//

// Solution144.cpp

// Algorithm

//

// Created by Pancf on 2019/12/21.

// Copyright © 2019 Pancf. All rights reserved.

//

#include "Solution144.hpp"

#include <stack>

using std::stack;

vector<int> Solution144::preorderTraversal(TreeNode *root) {

vector<int> rv;

if (!root) {

return rv;

}

auto cur = root;

stack<TreeNode *> st;

while (cur || !st.empty()) {

if (cur) {

//前序遍历则要保存当前结点的值，然后将结点压栈，向左走一步

rv.push_back(cur->val);

st.push(cur);

cur = cur->left;

} else {

//栈顶结点的左子树为空时，出栈，然后访问出栈结点的右子树

cur = st.top();

st.pop();

cur = cur->right;

}

}

return rv;

}