480.二叉树的所有路径

描述

给一棵二叉树，找出从根节点到叶子节点的所有路径。

您在真实的面试中是否遇到过这个题？  是

样例

给出下面这棵二叉树：

   1
 /   \
2     3
 \
  5

所有根到叶子的路径为：

[
  "1->2->5",
  "1->3"
]

递归先序遍历左子树即可。

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: the root of the binary tree
     * @return: all root-to-leaf paths
     */
    vector<string> binaryTreePaths(TreeNode* root) {
        // Write your code here
        vector<string> res;
        if(root==NULL) return res;
        binaryTreePathsCore(root,res,to_string(root->val));
        return res;
    }

    void binaryTreePathsCore(TreeNode* root,vector<string> &str,string strpath){
        if(root->left==NULL&&root->right==NULL){
            str.push_back(strpath);
            return;
        }
        if(root->left!=NULL)
            binaryTreePathsCore(root->left,str,strpath+"->"+to_string(root->left->val));
        if(root->right!=NULL)
            binaryTreePathsCore(root->right,str,strpath+"->"+to_string(root->right->val));
    }
};