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leetcode Binary Tree Preorder Traversal
实现前序遍历。可参见中序遍历Binary Tree Inorder Traversal
递归：
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public: void helper144(TreeNode *root, vector<int> &perm) { if (!root) return; perm.push_back(root -> val); helper144(root -> left, perm); helper144(root -> right, perm); } vector<int> preorderTraversal(TreeNode *root) { vector<int> perm; helper144(root, perm); return perm; }};
非递归：
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public: vector<int> preorderTraversal(TreeNode *root) { vector<int> perm; stack<TreeNode *> sta; TreeNode *p = root; while(!sta.empty() || p) { while(p) { perm.push_back(p->val); if (p -> right) sta.push(p -> right); p = p -> left; } if (!sta.empty()) { p = sta.top(); sta.pop(); } } return perm; }};
leetcode Binary Tree Preorder Traversal
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