二叉树的前序遍历
/** * Definition for a binary tree node. * 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 > vec; preOrder(root, vec); return vec; } //递归写法 /* void preOrder(TreeNode *root, vector<int> &path) { if (root) { path.push_back(root->val); preOrder(root->left, path); preOrder(root->right, path); } } */ //非递归写法 void preOrder(TreeNode *root, vector< int > &path) { stack<TreeNode *> TreeNodeStack; while (root != NULL || !TreeNodeStack.empty()) { while (root != NULL) { path.push_back(root->val); TreeNodeStack.push(root); root = root->left; } if (!TreeNodeStack.empty()) { root = TreeNodeStack.top(); TreeNodeStack.pop(); root = root->right; } } } };
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