145. Binary Tree Postorder Traversal

最新推荐文章于 2022-07-02 16:50:24 发布

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最新推荐文章于 2022-07-02 16:50:24 发布

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分类专栏： leetcode

本文链接：https://blog.youkuaiyun.com/sandrew0916/article/details/90732720

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1.C++ 递归：

Recursive solution

class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> nodes;
        postorder(root, nodes);
        return nodes;
    }
private:
    void postorder(TreeNode* root, vector<int>& nodes) {
        if (!root) {
            return;
        }
        postorder(root -> left, nodes);
        postorder(root -> right, nodes);
        nodes.push_back(root -> val);
    }
};

2.C++非递归：

class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> nodes;
        stack<TreeNode*> todo;
        TreeNode* last = NULL;
        while (root || !todo.empty()) {
            if (root) {
                todo.push(root);
                root = root -> left;
            } else {
                TreeNode* node = todo.top();
                if (node -> right && last != node -> right) {
                    root = node -> right;
                } else {
                    nodes.push_back(node -> val);
                    last = node;
                    todo.pop();
                }
            }
        }
        return nodes;
    }
};

python:非递归

def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res,stack=[],[]
        last=None
        while root or stack:
            if root:
                stack.append(root)
                root=root.left
            else:
                tmp=stack[-1]
                if tmp.right and last!=tmp.right:
                    root=tmp.right
                else:
                    res.append(tmp.val)
                    del stack[-1]
                    last=tmp
        return res