Leetcode|二叉树的属性|257. 二叉树的所有路径

1 DFS

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    
    
public:
    void dfs(TreeNode* root, vector<string>& path, string str) {
    
    
        if (!root) return;
        if (!root->left && !root->right) {
    
    
            str += to_string( root->val );
            path.push_back(str);
            return;
        }
        str += to_string( root->val ) + "->";
        dfs(root->left, path, str);
        dfs(root->right, path, str);
    }
    vector<string> binaryTreePaths(TreeNode* root) {
    
    
        vector<string> path;
        dfs(root, path, "");
        return path;
    }
};

2 BFS

这块其实要多维护一个记录每个节点下累计路径的队列，该队列和数的广度优先队列同步进出数据，当遇到叶节点时，原路径向量把当前叶节点对应的累计路径进行存储即可。

class Solution {
    
    
public:
    vector<string> binaryTreePaths(TreeNode* root) {
    
    
        vector<string> paths_vec;
        if (!root) return paths_vec;
        queue<TreeNode*> q_tree;
        queue<string> q_path;
        q_tree.push(root);
        q_path.push( to_string(root->val) );
        
        while (!q_tree.empty()) {
    
    
            TreeNode* node = q_tree.front(); q_tree.pop();
            string path = q_path.front(); q_path.pop();
            if (!node->left && !node->right) 
                paths_vec.push_back(path);
            else {
    
    
                if (node->left) {
    
    
                    q_tree.push(node->left);
                    q_path.push( path + "->" + to_string(node->left->val) );
                }
                if (node->right) {
    
    
                    q_tree.push(node->right);
                    q_path.push( path + "->" + to_string(node->right->val) );
                }
            }
        }
        return paths_vec;
    }
};