'lintcode 二叉树的前序遍历'

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lincode 二叉树的前序遍历

描述

给出一棵二叉树，返回其节点值的前序遍历。

样例

给出一棵二叉树 {1,#,2,3},

返回 [1,2,3].

思路

堆栈实现,先压入右儿子,再压入左儿子

代码

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/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: A Tree
     * @return: Preorder in ArrayList which contains node values.
     */
    vector<int> preorderTraversal(TreeNode * root) {
        // write your code here
        vector<int> res;
        if (!root) return res;
        stack<TreeNode *> s;
        s.push(root);
        while(!s.empty()){
            TreeNode *temp = s.top();
            s.pop();
            res.push_back(temp->val);
            if (temp->right)
                s.push(temp->right);
            if (temp->left)
                s.push(temp->left);
        }
        return res;
    }
};
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