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/** * 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> postorderTraversal(TreeNode* root) { vector<int> path; postOrder(root, path); return path; } /* void postOrder(TreeNode* root, vector<int> &path) { //递归写法 if (root) { postOrder(root->left, path); postOrder(root->right, path); path.push_back(root->val); } } */ void postOrder(TreeNode* root, vector<int> &path) { //非递归写法 stack<TreeNode *> TreeNodeStack; TreeNode *plastvisit = NULL; //记录结点是否访问过 while (root != NULL || !TreeNodeStack.empty()) { while (root != NULL) { TreeNodeStack.push(root); root = root->left; } root = TreeNodeStack.top(); if (root->right == NULL || plastvisit == root->right) { path.push_back(root->val); plastvisit = root; TreeNodeStack.pop(); root = NULL; } else root = root->right; } }};
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